Clays and Clay Minerals of Japan, #26 (Developments in Sedimentology)

DEVELOPMENTS IN SEDIMENTOLOGY 26

CLAYS AND CLAY MINERALS OF JAPAN

FURTHER TITLES IN THIS SERIES

VOLUMES 1 , 2 , 3 , 5 , 8 and 9 are out of print. 4. F.G. TICKELL T H E TECHNIQUES OF SEDIMENTARY MINERALOGY 6. L. VAN DER PLAS T H E IDENTIFICATION OF DETRITAL FELDSPARS 7. S. DZULYNSKI and E.K. WALTON SEDIMENTARY FEATURES OF FLYSCH AND GREYWACKES 10. P. McL. D. DUFF, A. HALLAM and E.K. WALTON CYCLIC SEDIMENTATION 11. C.C. REEVES JY. INTRODUCTION T O PALEOLIMNOLOGY 12. R.G.C. BATHURST CARBONATE SEDIMENTS AND THEIR DIAGENESIS 13. A.A. MANTEN SILURIAN REEFS OF GOTLAND 14. K.W. GLENNIE DESERT SEDIMENTARY ENVIRONMENTS 15. C.E. WEAVER and L.D. POLLARD T H E CHEMISTRY OF CLAY MINERALS 16. H.H. RIEKE 111 and G.V. CHILINGARIAN COMPACTION OF ARGILLACEOUS SEDIMENTS 17. M.D. PICARD and L.R. HIGH JY. SEDIMENTARY STRUCTURES OF EPHEMERAL STREAMS 18. G.V. CHILINGARIAN and K.H. WOLF COMPACTION OF COARSE-GRAINED SEDIMENTS 19. W. SCHWARZACHER SEDIMENTATION MODELS AND QUANTITATIVE STRATIGRAPHY 20. M.R. WALTER, Editor STROMATOLITES 21. B. VELDE CLAYS AND CLAY MINERALS IN NATURAL AND SYNTHETIC SYSTEMS 22. C.E. WEAVER and K.C. BECK MIOCENE OF T H E SOUTHEASTERN UNITED STATES 23. B.C. HEEZEN, Editor INFLUENCE OF ABYSSAL CIRCULATION ON SEDIMENTARY ACCUMULATIONS IN SPACE AND TIME 24, R.E. GRIM and N. GUVEN BENTONITES 25A. G. LARSEN and G.V. CHILINGAR DIAGENESIS IN SEDIMENTS AND SEDIMENTARY ROCKS

DEVELOPMENTS IN SEDIMENTOLOGY 26

CLAYS AND CLAY MINERALS OF JAPAN Edited by

TOSHIQ SUDQ Emeritus Professor, Tokyo University of Education, Tokyo 153, Japnn

SUSUMU SHIMQDA Institute of Geoscience, University of Tsukuba, Ibaragi Pref. 300-31, Japan

1978

KODANSHA LTD. Tokyo

ELSEVIER SCIENTIF PUBLISHING COMPP Amsterdam-Oxford-New

8

KODANSHA SCIENTIFIC BOOKS

Copyright @ 1978 by Kodansha Ltd. All rights reserved No part of this book may be reproduced in any form, by photostat, microfilm, retrieval system, or any other means, without the written permission of Kodansha Ltd. (except in the case of brief quotation for criticism or review) ISBN 0-444-41238-7 (series) Library of Congress Cataloging In Publication Data

Main e n t r y under t i t l e : Clays and c l a y minerals of Japan. (Developments i n sedimentology ; 26) (Kodansha s c i e n t i f i c books) Bibliography: p. Includes index. 1. Clay--Japan. 2. Clay minerals--Japan. I. SudO, Toshio, 191111. Shimcda, Susumu, 1935111. Series. QE471.3.C53 549l.6 78-8405 ISBN 0-444-99787-3

Copublished by KODANSHA LTD. 12-21 Otowa 2-chome, Bunkyo-ku, Tokyo 112 and

ELSEVIER SCIENTIFIC PUBLISHING COMPANY 335 Jan van Galenstraat, P.O. Box 211, Amsterdam, The Netherlands ELSEVIER NORTH-HOLLAND, INC. 52 Vanderbilt Avenue, New York, N.Y. 10017 Printed in Japan

Contributors

Keinosuke NAGASAWA, Geoscience Institute, Faculty of Science, Shizuoka University, Ohya, Shizuoka-shi 422, Japan Susumu SHIMODA, Institute of Geoscience, University of Tsukuba, Niiharigun, Ibaraki Pref. 300-31, Japan Haruo SHIROZU, Department of Geology, Faculty of Science, Kyushu University, Higashi-ku, Fukuoka-shi 8 12, Japan Toshio SUDO, Emeritus Professor, Tokyo University of Education, Setagayaku, Tokyo 156, Japan Hideo TAKESHI, Institute of Geological Sciences, Faculty of General Education, Osaka University, Toyonaka-shi 560, Japan Koji WADA, Department of Pedology, Faculty of Agriculture, Kyushu University, Higashi-ku, Fukuoka-shi 8 12, Japan

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Preface

Studies on clays and clay minerals have developed over a broad scope involving the basic sciences, industry and agriculture, and clay mineralogy has played an important role in clarifying the fundamental aspects. All such work is now organized into a single system, clay science, which involves a vast amount of published and collated information on an international scale. The clays and clay minerals are mostly natural materials, but include some artificial products. Clay and clay mineral synthesis is thus expected to increase in importance in the future. The properties of clays and clay minerals are more or less variable, as reflected in their crystal structures, thermal effects, and claywater systems. These variations in properties of course extend across different groups, but it is also not uncommon for species of the same group to show differences, a fact which has undoubtedly promoted academic interest in, and enhanced the industrial use of clays. The variations mostly result from the ability of clays and clay minerals to respond sensitively to changes in physical and chemical environmental conditions, both in nature as well as in the laboratory. The natural environmental conditions cover the formational and transformational processes of the clays in nature, as indicated by the results of clay synthesis and by geological and mineralogical studies on the modes of occurrence, mineral associations, textures and origins of clays. It should be noted that the modes of occurrence and origins of clays and clay minerals are essentially controlled by their geological environment, which is apt to vary geographically from region to region. Synthesized information on the geological and mineralogical properties of clays in each geographical region is thus pertinent to general studies on a regional as well as global basis. The main purpose of the present book is to provide an organized account of the geological and mineralogical properties of clays and clay minerals in Japan. Chapter 1 gives an outline of the historical development of clays and clay-mineral studies in Japan. Throughout, an attempt is made to summarize the studies putting them into perspective with the major research trends in the world, and imparting sometimes the classical but still useful knowledge as well as recent one. Subsequent chapters prepared by specialists in each field, then cover in detail the most important individual topics. Many cross-references are included so that a general view of the sub,iectcan readily be obtained. As editors, we wish to express our thanks to all authors and publishers who vii

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Vlll

PREFACE

have granted permission to reproduce published diagrams and photographs. We also acknowledge the generous help and advice of many friends and colleagues during the preparation of this book. Particular thanks are due to Mr. E. Tashiro and Mr. A.J. Smith of Kodansha for their editorial and linguistic assistance in the preparation of the final manuscript. August, 1977

Toshio SUDO Susumu SHIMODA

Contents

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Contributors Preface ........................................................................... Chapter 1.1. 1.2. 1.3.

v vii

.

1 An Outline of Clays and Clay Minerals in Japan Studies on Clays and Clay Minerals .......................................... Modes of Occurrence. Mineral Assemblages and Origins ........................ Clays and Clay Minerals ....................................................

1

20 33

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Chapter 2 Weathering of Volcanic Ash and Other Pyroclastic Materials .......................................... 2.1. Mineralogy of Volcanic Ash Soils 2.2. Deep Weathering of Pyroclastic Deposits ...................................... Chapter 3.1. 3.2. 3.3. 3.4.

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3 Wall Rock Alteration of Kuroko Deposits KurokoDeposits Alteration Patterns Clay Minerals ......................................................... Conclusion

........................................................... ....................................................... ..............................................................

105 114 127 130 136 143

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Chapter 4 Allophane and Imogolite 4.1. Chemical Composition ...................................................... 147 4.2. Optical Properties .......................................................... 151 4.3 Electron Microscopy ........................................................ 152 4.4. X-Ray and Electron Diffraction .............................................. 157 4.5. Thermal Analysis .......................................................... 160 4.6. Infrared Spectra ............................................................ 163 4.7. Charge Characteristics ...................................................... 167 4.8. Surface Acidity ............................................................ 170 4.9. Electrophoresis and Dispersion-Flocculation .................................. 172 4.10 Coordination Status of Aluminum ............................................ 173 4.1 1. Anion Sorption ........................................................... 174 4.12. Surface Area ............................................................ 178 4.13. Density and Porosity ...................................................... 179 4.14. Structure Models .......................................................... 180

.

Chapter 5.1. 5.2. 5.3.

5 Kaolin Minerals Dickite and Nacrite ........................................................ Kaolinite and Halloysite .................................................. ................................................................ Genesis

Chapter 6.1. 6.2. 6.3.

6

189 193 212

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Smectites Montmorillonite .......................................................... Saponite .................................................................. Nontronite ................................................................

ix

221 237 239

CONTENTS

X

6.4.

Stevensite

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240

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Chapter 7 Chlorite Minerals 7.1. Outline of Trioctahedral Chlorite Minerals .................................... 7.2. The FeMg-chlorites of Schists and Mg-chlorities of Serpentinites and Certain Metallic Ore Deposits ...................................................... 7.3. Fe- and FeMg-chlorites of Hydrothermal Metallic Ore Veins .................... i.4. Ferromagnesian Chlorite Minerals in Miocene Tuffaceous Sediments .............. 7.5. Magnesian Chlorite Minerals in Altered Wall Rocks of Kuroko Deposits 7.6. Dioctahedral Chlorite Minerals

.......... ..............................................

243 244 247 251 253 259

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Chapter 8 Interstratified Minerals 8.1. Modes of Occurrence of Interstratified Minerals ................................ 8.2. The Mineralogical Properties of Interstratified Minerals ........................ 8.3. Origin of Interstratified Minerals ............................................ Subject Index

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265 275 312 323

Chapter 1 An outline of clays and clay minerals in Japan Toshio SUDO

The present Chapter attempts to summarize studies on the clays and clay minerals of Japan. The first half covers the basic work up to the present, with brief comments on major trends in related work overseas. It involves research on (1) the specific properties of clay minerals as revealed by X-ray, thermal, electron optical analyses, etc., (2) some of the analytical procedures, (3) synthesis, (4) changes in the properties of clays and clay minerals on heating, grinding, and chemical treatment, and ( 5 ) miscellaneous items. The latter half of the Chapter attempts to survey the mineralogical properties, modes of occurrence and origin of the clays and clay minerals found in Japan. Throughout geological time, volcanic activity has frequently and actively occurred in Japan, resulting in an abundance of clays and clay minerals which occur as hydrothermal alteration products of various rock types, and as weathering products of volcanic ashes and glassy tuffs.

1.1.

STUDIES ON CLAYS AND CLAY MINERALS

1.1.1. Historical deve!opment

In 1899, a clay having a strong bleaching effect was discovered at Odo, Niigata Prefecture (Higashi-kambara-gun), and K. Kobayashi-a late Emeritus Professor of Waseda University-began research on the clay (the so-called “Kambara earth”) to test its importance to the petroleum industry. He first noticed that the clay had acidity, and so termed it an “acid clay”. Studies in this field, particularly on the clay chemistry and significance to petroleum engineering, then developed as his life work (Kobayashi, 1912,1929).The full range of studies undertaken by Kobayashi’s group has been described in his book, Sansei-Hakudo (Acid Clay), 1st ed., Maruzen (Kobayashi, 1919). In the early stages, Kobayashi devoted himself to the clarification of the nature of the observed clay acidity, and even in those days, he approached close to modern concepts. He extended the studies on the basis of the exchange acidity (in modern terminology) by confirming the release of alumina on treatment with neutral salt solution, and pointed out the important role of alumina in the clay acidity. At 1

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this stage, he shared common interests and aims with workers in inorganic, organic, and colloid chemistry, and with soil scientists devoted to the clarification of the nature of the acid soils in Japan. Numerous interesting properties of the acid clays were revealed as follows : (1) a strong ability to dehydrate, (2) a strong adsorptive ability for various kinds of materials such as vitamin B, (3) a catalytic ability for various organic chemical reactions involving dehydration, polymerization, isomerization, condensation, and cracking distillation, and (4) color-forming reactions with substances such as benzidine, vitamin A, and carotene. It is worthy of note also that Kobayashi, on the basis of these properties and the modes of occurrence and origin in nature, proposed his own concept for the origin of petroleum. He and his collaborators thus laid the foundation for the acid clay industry, and stimulated a broad interest in studying clays in other areas such as geology, mineralogy, and the soil sciences. The mining of bentonite is thought to have begun at Wyoming, N. America, in around 1888. About 20 yr later in Japan, exploitation of bentonite was commenced in Yamagata Prefecture. In 1930, R. Shigemune of the Government Chemical Industrial Research Institute confirmed the identity of the Japanese material with the bentonite occurring in the U.S.A. The thermobalance originally designed by K. Honda-a late Emeritus Professor of Tohoku University-set the way for work in the field of thermogravimetry (TG), and numerous thermogravimetric studies on various kinds of materials including clays and clay minerals followed (e.g. Kobayasi, 1940; Saito, 1969). S . Kozu-a late Emeritus Professor of Tohoku University-and his collaborators (Satoh, 1923; Kozu and Masuda, 1926), undertook thermal studies on kaolin clays and other related minerals, presenting DTA (differential thermal analysis) and T G curves and data for thermal expansion and contraction. Most of the curves were recorded up to temperatures exceeding 1000°C, and included data for both heating and cooling (Fig. 1.1). This work can be regarded as the pioneering thermal study on clays and clay minerals in Japan, and is widely known together with the research on the feldspar problem which Kozu and his group also performed. J. Takahashi-a late Emeritus Professor of Tohoku University-and his collaborators carried out extensive studies on glauconite, including its mineralogical properties and origin (Takahashi and Yagi, 1929;Yagi, 1929,1930,1932a). This work is regarded as the pioneering clay mineralogical study from the viewpoint of sedimentology in Japan. In the field of soil science, there was a comparatively long history of studies on soil clays in Japan. Since around 1910, work on soil acidity was actively undertaken by several soil scientists such as G. Daikubara, S. Osugi and T. Seki, contemporaneously with the work of K. Kobayashi. Seki (1913,1928) later investigated a considerable number of volcanic ash soils in Japan and pointed out several common chemical features among them, such as their remarkable deficiency of silica and base, the existence of “free” alumina and the strong “absorptive

STUDIES ON CLAYS A N D CLAY MINERALS

3

Fig. 1.1. The original DTA curve (“heating curve”) for kaolinite published by Kozu and his collaborators (Satoh, 1923). Inert material: alumina (upper graph), feldspar (lower graph).

power” for phosphoric acid. These features were considered to derive from allophane. Shioiri (1934, 1935) studied the properties of a gel-like material occurring as thin films in the interspaces of weathered pumice fragments, and reported it to be “allophane”. It is considered that this material might be imogolite. Further, Shioiri began work on the electrokinetic properties of soil clays in Japan. Kawamura and Funabiki (1936) studied the chemical composition and X-ray powder diffraction patterns of soils derived from various kinds of rocks in Japan, and pointed out the prevalent distribution of halloysite minerals in the samples studied. Attention should also be given to the work of Tamamushi on the colloid chemistry of clays and clay minerals such as acid clays, bentonite, etc., as described in his extensive reports on colloid chemistry (e.g. Tamamushi, 1937). The earlier investigations mentioned above are all regarded as cornerstones of the research on clays and clay minerals undertaken in Japan. The following sections introduce the subsequent work by Japanese workers, sometimes in collaboration with foreign workers, in relation to the major research trends in the world. 1.1.2.

X-ray studies

Since early days, studies on the crystal structure of clay minerals in the form of micron-sized flakes have been made by inspecting the X-ray powder diffrac-

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tion data and making reference to the results of crystal structure determinations of macro-crystalline analogs of the clay minerals. Advanced studies have revealed that although in many respects there are strong family resemblances, clay minerals in general show a variability in crystal structure, as illustrated by the existence of many polytypes and of order-disorder structures having distorted crystal lattices and disordered stacking of the layer lattices. This variability may affect the X-ray diffraction spots or lines, giving rise to modifications in spacing, intensity, and line profiles. Hendricks (1940), analyzing the continuous scattering of X-rays by certain clay minerals, clarified the nature of their disordered structures in terms of lattice distortion and random displacement of the layer lattices, which may occur within a wide range of order-disorder, particularly in random shifts of multiples of b/3 along the 6-axis. Brindley and Robinson (1948) analyzed the line profiles of halloysite (7A). Subsequently, studies on the disordered crystal structures of clay minerals have advanced remarkably under the influence of Brindley and MCring (1951, 1953). Nakahira (1952) analyzed the line profile of the X-ray diffraction bands of montmorillonite, and suggested that it is best explained as comprising regions of local ordering, with random displacements at multiples of b/3. The structure of dickite was refined by Neuwham and Brindley (1956) and that of kaolinite by Brindley and Nakahira (1958a). In these refined structures, the departure of the tetrahedral and octahedral sheets from the ideal structural arrangement was clearly demonstrated. Bailey and his collaborators extended our knowledge of the crystal structures, crystal chemical properties and polytypes of chlorite minerals. Shirozu (1958), in his extensive work on chlorites in Japan, provided evidence for the orthogonal type in iron-rich chlorites, as first suggested by Engelhardt (1942). The crystal structures of an orthogonal chlorite and a twolayered Mg-vermiculite have been analyzed by Shirozu and Bailey (1965, 1966). Mention should also be made of the research on the refined crystal structures of certain phyllosilicates such as brittle mica (e.g. Takeuchi, 1965) and micas as reported by Takeda and his collaborators (e.g. Takeda and Donnay, 1966). All these studies served to promote crystal structural studies on clay minerals. Hendricks and Teller (1940) first presented a general formulation for the X-ray diffraction intensity of interstratified clay minerals. MacEwan and his collaborators (MacEwan, 1956, 1958; MacEwan and Ruiz Amil, 1959) prepared many calculated X-ray diffraction patterns and peak migration curves, and proposed the Fourier transform method, facilitating the analysis of interstratified structures. Kakinoki and Komura (1965) presented the most general formulation, which is not limited to scattering in any one direction, is applicable to any number of components and total number of layers in the crystallite, and takes into account the scattering due to interlayer material. Sat0 (1969), using the Kakinoki-Komura formulation, prepared many diagrams, and his work permitted the analysis of interstratified structures in a stricter sense than ever before.

STUDIES ON CLAYS AND CLAY MINERALS

5

As a result, Sat0 and Kizaki (1972) discovered a mica/montmorillonite interstratification having “Reichweite” (range of correlation), g = 2. Recently Nakajima, Watanabe and Sudo (1972) have reported the analysis of the line profiles of certain clay minerals using the method of Warren and Averbach (1950), and the small angle scattering of some clay minerals has been reported by Watanabe (1968).

1.1.3. Electron optical studies The methodology for the crystal structure analysis of fine crystal flakes of clay minerals using electron diffraction patterns was developed by Russian workers (e.g. Zvyagin, 1967). Honjo, Kitamura and Mihama (1954) performed single crystal, electron diffraction studies of a sample of “Hong Kong kaolin” (halloysite (7A)) and reported the following significant facts. (1) The majority of about 160 crystallites had the b[01] axis as the tube axis. (2) Some three-dimensional order was indicated in the structures, which appeared to be higher than that of halloysite. (3) The c-parameter was doubled, so that the structure contains two kaolin layers in the unit cell. Among the many electron micrographs of clay minerals, particularly interesting shapes are observed in the case of imogolite and spherulitic halloysite (allophane-halloysite spherules). (p. 80) The design of electron microscopes has recently been improved remarkably, and high resolution electron microscopy now permits the observation of fine lattice images and discussion of the fine structures. Yada (1963) studied chrysotile with a high resolution electron microscope and clarified several interesting inner textures of the chrysotile fibers. He pointed out that the observed dislocation patterns suggest the c-parameter as 7.3 A instead of 14.6 A, and that the lattice images observed in cross sections of the fibers exhibit multi-spiral lattice fringes instead of concentric ones. These findings may support the model proposed by Jagodzinski and Kunze (1954). Suito, Arakawa and Yoshida (1969) revealed fine layer structures of certain organomontmorillonites, e.g. the octadodecylammonium complex, in which clear lattice images such as at 40, 27, and 15 A were observed. Dislocations were also revealed in places. Recently, Nishiyama and Shimoda (1974) have studied the oblique texture electron diffraction pattern of certain micas and their interstratifications. These authors pointed out that the polymorphs such as 2M1 and 1M can be decided by indexing the resolved arcs along ellipses. An interstratified mineral with a small amount of expandable mineral layers shows an oblique texture pattern consisting of diffused arcs which are especially diffused along an inner ellipse. Other interstratified minerals having increasing ratios of expandable mineral layers tend to show continuous scattering along ellipses with several maxima which could be assigned to the characteristic reflections of each of the polymorphs. This continuous scattering is probably due to several factors such as stacking

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disorder of dehydrated expandable layers, the superstructure, and a strained structure which may result from dehydration of expandable layers and/or mechanical bending of very thin plates of crystallites. 1.I .4.

Thermal analysis

The technique of differentialthermal analysis (DTA) has been used by scientists for many years. Since around 1945, it has been actively developed in many countries and a range of equipment of new or improved design has been produced in such countries as France, Great Britain, Hungary, Japan, the U.S.A., and U.S.S.R. In Japan, as mentioned above, excellent thermal studies on kaolin clays and related substances were carried out by Kozu and his collaborators in the period 1923-26. Since around 1945, active DTA studies have been made on broader aspects involving ceramics, the chemical industry, and mineralogy (Sudo, Nagasawa, Amafuji et al., 1952), and in Japan, DTA has subsequently been used not only in studies of clays but also in mineralogy in general. In Japan, as already mentioned, thermogravimetry (TG) originated from the thermobalance designed by Honda (1915). Since then, TG has been extensively used for studies on various kinds of materials including clays. In most cases, TG curves of clays and clay minerals are now recorded with a simultaneouslyrecording DTA-TG apparatus, or in some instances DTA-TG-DTG (delivatograph), and TG is frequently employed for the determination of the activation energy of decomposition or dehydration. The progress in thermal analysis since around 1954 stems directly from the establishment of new methods and new equipment, such as the differentialthermogravimetry (DTG) developed by Keyser (1953) and the delivatograph-a simultaneously recording DTA-TG-DTG apparatus designed by Paulik, Paulik and Erdey (1958). Recently, in Japan, apparatus such as the delivatograph (Saito, Otsuka, Iwata and Tsuchimoto, 1964), scanning calorimeter, high temperature or low temperature DTA apparatus, and simultaneously recording DTA apparatus and X-ray powder diffractometer, has been used for studies on various kinds of materials including clays and clay minerals. 1.1.5. Infrared analysis

Following the pioneering work of Keller and Pickett (1949), infrared analysis has been extensively employed for research on clays and clay minerals. In Japan, the major reports include those on the identification of kaolin minerals in the presence of chlorite (Kodama and Oinuma, 1963), interstratified minerals (Oinuma and Hayashi, 1965), and chlorites (Hayashi and Oinuma, 1965, 1967).

1.I .6. Optical studies Marshall (1930, 1935) developed a technique for measuring the mean refrac-

STUDIES ON CLAYS AND CLAY MINERALS

7

tive index and electronic birefringence of fine mineral particles. Shioiri and Fukuzawa (1951), using Marshall’s method, obtained optical data for certain soil clay minerals in Japan. They pointed out the wide difference in optical properties between the fine particles in “silicic soils” composed largely of montmorillonite and those in “aluminous soils” composed largely of halloysite (7A). 1.I .7. Thin section studies

In soil micromorphology, it is important to examine the microtexture of soils by observing thin sections under a polarizing microscope. Kubiena (1938) established a system for this purpose. Numerous reports have subsequently been published on the methodology for preparing thin sections of clays and soils. Matsui (1966) pointed out that an improved procedure based on the method proposed by Altemuller (1962) was satisfactory, and using this method, he successfully performed micromorphological studies on the “heavy soils” (pseudogley) of Hokkaido. The unsaturated polyester resin “Polylite J 8157” is diluted with an almost equal volume of monostyrol, and small amounts of methylethylketone peroxide and cobalt naphthate, a catalyst for polymerization, are added. The resultant solution is impregnated into soil specimens under near vacuum conditions. About 10-15 hr for “heavy soils” and 2-3 hr for “light soils” is required for the resin solution to penetrate into the specimens. After cessation of bubbling, the suspensions are allowed to stand at room temperature for a few days. They are then dried in an oven at a temperature below 40°C,and cooled in room air for 1-2 days to ensure complete consolidation. 1.I .8. Electrokinetic studies

Watanabe (1966) carried out research on the electrophoresis of certain clay minerals such as kaolinite, halloysite (7A) (a sample of “Hong Kong kaolin”), montmorillonite, mica, and allophane, and the data obtained were subejcted to statistical treatment. He pointed out that allophane saturated with sodium ions shows an isoelectric point at about pH 6.7. Above this value, the particles move towards the anode, and below it, they move in the reverse direction. Based on the statistical results, he concluded that the speed of allophane particles is more variable than that of other clay minerals, and suggested that allophane particles are non-uniform in terms of their particle size and zeta-potential. 1.I .9. N M R (nuclear magnetic resonance)

The magnetism of matter originates from two sources: electrons and the atomic nucleus. When an atomic nucleus is placed in a magnetic field, it absorbs energy from or discharges energy to the external electromagnetic field. This represents the basis of nuclear magnetic resonance (NMR). Kitagawa (1972) studied the NMR of adsorbed water and hydroxyl groups of minerals such as allophane, kaolinite, halloysite (10 A), and montmorillonite, and found a distinct

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difference in energy levels between the adsorbed water and hydroxyl groups in kaolinite, halloysite and montmorillonite. However, such a distinction was difficult with allophane. 1.1.10. Mossbauer eflect

Mossbauer (1958) discovered a phenomenon in which y-rays are scattered from an atomic nucleus without recoil, and are adsorbed by resonance into atomic nucleii of the same kind. This is known as the Mossbauer effect. The behavior of scattering without recoil produces absorption spectra. Two parameters indicate the position and resolution of the absorption spectra. These are the isomer shift (I.S.) and quadrupole splitting (Q.S.).They vary with the following factors : the degree of oxidation, electron configuration, coordination number, and site symmetry of the ions in the crystal structure. The Fe3+/Fe2+ratio can be obtained from the area of the absorption bands. Kohyama, Shimoda and Sudo (1973), with assistance from H. Sano, Ochanomizu University, studied the Mossbauer effect in the clay occurring as an alteration product of volcanic rock fragments in Oya-ishi. This material is composed of iron-rich saponite and ironbearing montmorillonite, and is easily oxidized when exposed to daylight. There was no marked difference in I.S. and Q.S. of Fe3+between the unoxidized and oxidizedparts. The Q.S.value of Fez+decreased with increasing degree of oxidation, suggesting that the site symmetry or structural environment of the iron ions is more symmetrical in the oxidized than in the unoxidized state (p. 46). 1 J.11. EPMA (electron probe microanalyzer)

Recently, EPMA has been developed for use in the study of clays and clay minerals. Kohyama, Shimoda and Sudo (1973) performed step-scanning analysis and quantitative analysis of the clay from Oya mentioned above. This clay gives the X-ray powder diffraction pattern of montmorillonite minerals. Under the microscope, it exhibits a vesicular texture, and the vesicules are entirely altered to clay minerals. There is a slightly difference in microscopic appearance between the marginal and core parts of each vesicule. By EPMA, Kohyama et al. clarified that the marginal part is composed of iron-bearing montmorillonite and the core part of iron-saponite (p.46). Tazaki and Tazaki (1975) analyzed a weathered product of biotite using EPMA. This material has a vermicular shape and is found in weathered pumice layers and pyroclastic flows intercalated in the Daisen Loam. 1 ts color ranges from ivory-white to brown as a whole, but on ~10s:: examination, each vermicule can been seen to consist of white and brown bands which usually exhibit rather irregularly mixed layering. Using EPMA, with the aid of X-ray and thermal analysis, they concluded that the vermicules are composed of minerals such as hydrobiotite, kaolinite, gibbsite, and probably Alinterlayer vermiculite. 1.1.12. Surnpje preparation

The methods of sample preparation of clays and clay minerals in Japan in-

STUDIES ON CLAYS AND CLAY MINERALS

9

volve the usual sieving, dispersion, sedimentation, etc. However, on detailed points such as the kind and concentration of dispersing reagents, there are some slight differences among workers in different fields. In many reports published in Japan, the fraction of less than 2 P is defined as the clay fraction, and the dispersing reagents used often include ammonia, sodium hydroxide, sodium silicate, “Calgon,” etc. Routine procedures have been proposed in some fields such as agriculture and soil engineering. As is well known, it is extremely difficult to separate the clay fraction into finer fractions each composed of one kind of clay mineral in the purest possible state. In order to circumvent this problem, a general procedure has been developed which serves to differentiate and identify each clay mineral constituent in complicated clay mineral mixtures without separation. Concerning the preparation of the clay fraction, it should be remembered that the clay minerals are in general very sensitive to chemical treatment. In the course of sample preparation, various kinds of reagents may be used to induce dispersion of the clay particles or to remove iron oxides, hydroxides, organic matter, etc. There is always the possibility that the chemicals may modify the properties of the original clay minerals themselves. Careful examination of such effects on test samples is thus important. Particular attention has been paid in Japan to sample preparation from volcanic ash soils which, in some instances, disperse well under acidic conditions, in contrast to the usual clays which tend to disperse well under alkaline conditions. Kanno (1954) has established an analytical method as described next. Abundant organic matter is commonly present in volcanic ash soils. i t is thus usually necessary to employ considerable amounts of hydrogen peroxide to remove such organic matter, and so to determine the amount of iron and aluminum in the filtrate obtained after treatment with hydrogen peroxide, since small amounts of R203 (of the order of 2-4%) tend to be dissolved by the oxalic acid formed during digestion of the sample in hydrogen peroxide. The powder obtained after treatment with hydrogen peroxide is dried in room air. A small fraction is digested in 0.002 N HC1 or 0.008 N NaOH, and its dispersingability in each case is examined. if there is better dispersion in HCl than NaOH, the following procedure is adopted. About 10 g powder is digested in 10 ml of 1 N HCI, to which water is added to make the volume up to 100 ml. The mud so obtained is allowed to stand for about 1 hr, with occasional stirring, and then successively filtered with a collodion membrane. The Si02 and AI2Q in the filtrate are determined, and the amounts are added to the wt % of the clay fraction obtained at the final stage of analysis. The powder on the filter membrane is passed through a 0.2 mm sieve, and the residue on the sieve is dried and weighed. The finer fraction passing through the sieve is made up as a suspension in water (final volume, about 200 nil), to which 2 ml of 1 N MC1 is added. The mud so obtained is transferred completely to a shaker and shaken for several hours. The contents are then transferred to a I-liter sedimenting cylinder and the volume is made up to about 500 ml with water. The resultant :uspension is

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10

shaken with an electric shaker for about 10 min, and the suspended particles are analyzed in the usual way. 1.1.13. Identification and quantitative estimation of the clay minerals in clays Clays usually consist of several different kinds of clay minerals intimately mixed with one another. In all studies of clays and clay minerals, it is of course necessary to identify the nature and determine the amounts of each constituent clay mineral. However, separation of the clay into its clay mineral constituents by mechanical means is extremely difficult. Moreover, particularly in fields such as geology, soil science and engineering, it is generally necessary to survey numerous clay samples. The method used should thus satisfy the following basic condition: to be able to identify the properties and determine the amounts of each clay mineral in the individual clay sample in detail and as rapidly as possible. In other words, it should provide basically accurate data which can be utilized for routine work. A number of suitable quantitative methods have been proposed, such as by Hathaway and Carroll (1954), Johns, Grim and Bradley (1954), Schultz (1960), etc. In Japan, from about 1950, Oinuma and Kobayashi and their collaborators have compiled and developed a general scheme for the identification of the clay minerals in clays (Table 1.1), and have proposed a new method for estimating the relative proportions (Sudo, Oinuma and Kobayashi, 1961; Oinuma and Kobayashi, 1966). The procedure for rapid quantitative analysis is described next. A calibration curve is made with a mixture of clay minerals A and B and calcite powder (less than 5 The intensity of a particular peak in each of the minerals ( I Aand Is) is determined with reference to the intensity of the 3 peak of calcite, which is admixed in specific proportions in the test samples. In most cases, the calibration curve gives a near-linear relation. Assuming linearity, the weight ratio of the minerals A and B is obtained as (IA/iA):(IB/iB),where iA:iB is the intensity ratio of A and B when existing in equal amounts. From the calibration curves of mixtures of various pairs of clay minerals taken as standards, the intensity ratio of the basal reflections of selected standard clay minerals can be summarized as

e).

: '(10L-Mo') : '(144-CU : z(104-Mi): z ( 7 i - K ) 2.6:0.9:0.5:1.0:1.2 . . . Slit system 1"- lo-0.4 mm 3.6:0.9:0.7:1.0:1.0 . . . Slit system 1/6"-1/6"-0.4mm, where (15 A-Mo) = 15 A peak of montmorillonite, (10 A-Mot) = 10 A peak of dehydrated montrnorillonite, (14 A-Ch) = 14 A peak of chlorite, (10 A-Mi) = 108,peak of mica, and (7 A-K) = 7 A peak of kaolinite. The weight ratio of these minerals can then be expressed as '(15hfO)

I(Mi) L(&!l. I(Mo') _ . _ _ .I(Ch) -. -. i(Mo)

*

i(Mo')

*

i(Ch)

*

i(Mi)

I(K) __ *

i(K)

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11

TABLE 1.1. Procedures for the identification of clay minerals (Oinuma and Kobayashi, 1966)

XRA (Mo,Mi,Ch,V,K) -Higher resolution scans of 24-26”(28) . .XRAl) K,Ch -Heated to 150, 300, 450,600 and 750°C ... .XRA Mo,Mi,Ch,V,H -Treated with ethylene glycol or Mo,H,(Ch,Mi) glycerol ......XRA Ch,K -Treated with HCI ................... .XRAz) -Treated with ammonium nitrate solution. ......... .XRA3) V Clay fraction --Treated with sodium citrate, calcium AI-V chloride and glycerol ... XRA4) DTA K,(Ch,Mo,Mi,V) Mo -Treated with piperidine ..............DTAS) Infrared spectral analysis6) K Electron micrographic observations (K) Chemical analysis Staining test?) Mo Cation exchange capacity (Mo,V)

The amount of each test sample is fixed at 0.04 g in total. The sample is placed on a slide glass and an appropriate amount of water is added to give a mud. This is gently spread over an area, 2.0 x 2.7 cm, with a matchstick, and allowed to stand in room air without disturbance. A thin clay film is then formed on the slide glass by drying. This technique is tentatively called the “natural setting method.” The addition of excess water tends to create aggregates, and these are difficult to develop into a uniform state. The alternative procedure of adding water drop-wise and stirring gently with a matchstick is usually effective for avoiding bubble formation. If bubbles are formed, they may be removed by suction in a vacuum. If difficulty is encountered in obtaining a uniform state in the clay mud, tapping lightly is often effective. Generally speaking, it is difficult to get a perfect orientation of the clay mineral flakes. Rubbing a paste strongly between two glass slides is effective in obtaining a well-oriented state, but this method gives poor reproducibility as regards uniformity of thickness. The above technique of natural setting, although not giving a perfect orientation, is thus recommended due to its good reproducibility for obtaining a uniform state.

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1.I . 14. Kinetics

Recently, Tsuzuki and his collaborators have extended their studies on hydrothermal alteration on the basis of laboratory experiments and chemical kinetics carried out on the side of an open system. The work concerns chemical reactions involving material transfer and complicated kinetic processes controlled not only by the reaction temperature but also by chemical compositional changes in the reacting solution. The process of rock alteration caused by a solution in an open system can be described in general terms as follows. The solution at a given locality reacts with thecoexistent rock. With timelapse, thecompositions of both the rock and the solution change. The solution with modified chemical composition also migrates successively to adjacent areas where it again reacts with the local rock (Tsuzuki and Mizutani, 1971). Tsuzuki, Mizutani, Shimizu and Hayashi (1974) treated potassium-feldspar with acidic solutions containing H and K at various concentrations in a silica glass tube at 210-270°C. The results were analyzed kinetically assuming A1 to be inert and silica to be mobile. The results suggest a process in which once-dissolved silica is later precipitated, when it remains after kaolinite formation. The process is able to explain many examples of rock alteration in nature. Kajiwara (1973), using the thermochemical data of Helgeson (1969), has extended the studies towards predicting possible assemblages of stable minerals in marine sediments. Concerning clay minerals, he suggested that Mg-montmorillonite, Mg-chlorite and probably talc, may be stable dependent on the activity of silica and alumina. The following concepts were developed. (1) The essentially uniform chemical state throughout the oceans as regards pH and concentrations of major cations presents certain limitations to the stable mineral assemblages. (2) The sea water is approximately in chemical equilibrium with, and thus buffered by the marine sediments due to the occurrence of rapid cation-exchange reactions. Kajiwara also suggested that the hydrothermal ore-forming solutions responsible for the so-called Kuroko type of mineralization (p. 23) may have derived essentially from cyclic coeval sea water. On the basis of the above assumptions, Kajiwara predicted the occurrence of stable mineral assemblages in the hydrothermal system of the earth’s crust under conditions where the sea water and rock-forming minerals have interacted at elevated temperature. 1.1.15. Synthesis

Studies on the synthesis of clay minerals from inorganic gels or various parent minerals under hydrothermal conditions were begun in about 1935, such as by No11 (1935) and Ewe11 and Insley (1935). Numerous reports have been published since that time. In Japan, Otsubo and Kato (1954) synthesized montmorillonite and Zn-montmorillonite using silica, alumina and magnesia gels, and zinc hydroxide as starting materials. Koizumi and Roy (1959) synthesized montmorillonites with different cation-exchange abilities employing a starting material

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consisting of gels with the chemical composition of beidellite or saponite. Iiyama and Roy (1963) synthesized an interstratified mineral (“illite-saponite”) from inorganic gels. Ueda and Sudo (1966) studied a new and interesting method for the synthesis of interstratifications of mica and expandable minerals. These authors treated micas such as fine-grained white micas and coarse-grained muscovite or phlogopite flakes, with chemicals such as aluminum sulfate and magnesium carbonate under hydrothermal conditions. They found that the micas could be converted to interstratifications which, dependent on the experimental conditions, were variable as regards the nature of their expandable mineral layers and regularity of the layer stacking, from completely regular to more or less random. They also reported that when potassium alum was used in addition to the above chemicals, a completely regular type of mineral closely resembling natural material could be produced. It is of interest to note that as the formation of these interstratifications proceeded, so the crystallization of alunite occurred in the residual liquid. Tomita and Sudo (1968) reported another interesting synthesis of interstratifications from micas. They found that micas such as fine-grained white micas and fine powders of coarse-grained muscovite flakes could be converted readily to interstratifications of mica and expandable mineral layers when the micas were heated to temperatures sufficiently high as to cause dehydroxylation, and then successivelydigested in warm HCI. The products obtained were diverse in terms of the nature of their expandable mineral layers and regularity of the layer stacking, from completely regular to more or less random. When the regular product was further digested in magnesium chloride solution, it approached closer to a natural regular interstratification in its overall properties. Tomita and his collaborators have extended such studies and reported that similar results were obtained when the micas were treated in a molten lithium salt (Tomita and Sudo, 1971), or when they were dehydroxylated and then digested in NaTPB (sodium tetraphenylboron) (Tomita and Dozono, 1972). These authors suggested that the process of formation of the interstratifications in their experiments, and also those in the experiments of Ueda and Sudo, may indicate an electric polar hypothesis for the origin of the interstratifications (see section 1.3.18). Recently, Nagasawa, Brown and Newman (1974) have carried out detailed research on the products obtained after boiling biotite flakes in 0.2 M AlCL solution. The product exhibited a 14 A spacing which was unchanged after K-saturation or ethylene glycol treatment, but gradually collapsed on heating. After removal of the interlayer material with sodium acetate, K-saturation caused a collapse to 10 A. In this respect, the product is close to the weathering product of biotite reported by Kato (1965) as trioctahedral Al-interlayer vermiculite. The structure type is two-layer monoclinic with a P-angle of 97”, and the stacking sequence is an alternation of Ia-4 and Ia-6 chlorites (notation follows that reported by Bailey and Brown, 1962). In this respect, the product accords

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with natural macroscopic vermiculite. The interlayer material is composed of A1 associated with H 2 0 and (OH), and is therefore intermediate between the interlayer materials of vermiculite and chlorite. 1.1.16 High temperature phases of Kaolin minerals

Kaolin clays represent one of the most important raw materials in the high temperature inorganic industries. The nature of the high temperature phases of kaolin minerals is thus of great importance, and numerous studies have been carried out in this field due to the complexity of the problem and the frequent lack of any broad consensus of opinion. Brindley and Nakahira (1958b) reported that the y-aIumina phase is really composed of silica and alumina in the form of a spinel structure, i.e. a silicaalumina spinel. Brindley and Nakahira (1959) on the basis of the new concept, accounted for the mullite formation occurring at 140OOC as a process in which silica-alumina spinel decomposes to mullite of the aluminum-rich type and the resultant excess silica crystallizes out as cristobalite. Tsuzuki and Nagasawa (1969) carried out detailed studies on the high temperature phases occurring in the 900-1000" C region. They concluded that several forerunning reactions, such as thermal expansion, increase in alumina with the tetrahedral coordination, and development of electron diffraction spots, took place before the peak temperature of the last exothermic peak was reached. Iwai, Tagai and Shimamune (1971) performed a crystal structure analysis of heated dickite and showed its dehydroxylated state on an electron density map. The inner (OH) tends to be dehydroxylated after the outer (OH).

I .I .17. Grinding efsects In 1953, Mackenzie and Milne (1953) gave data on the grinding effects of muscovite, biotite and vermiculite. Takahashi (1 959) also performed extensive studies on the grinding effects of minerals such as quartz, kaolinite, halloysite, (10 A), montmorillonite, mica, talc, and pyrophyllite. He followed in detail the changes in properties of these minerals with increasing grinding time, up to 200-500 hr. The findings may be summarized as follows. (1) The particle sizes gradually decreased, and the structures gradually disintegrated. (2) After grinding for 200-500 hr, the particles were finally transformed into completely spherical particles of uniform diameter, although the latter of course depended on the actual time of grinding and the kind of clay mineral used. (3) The amount of adsorptive water, and the solubility in acids or alkalies tended to increase on grinding. (4) The cation-exchange capacity also tended to increase, but approached a maximum after 50-100 hr, beyond which it either decreased (halloysite and kaolinite) or remained virtually unchanged (other minerals). 1.1.18. Clay-water systems

In the field of ceramics, soil engineering and agriculture, too many reports

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15

concerning clay-water systems exist for any simple synthesis to be made here. However, particular attention should be given to the extensive work of Y. Shiraki which has been widely reported in the literature. Also, the excellent studies of Okuda and Williamson (1964) in the field of ceramics, and of Kuwabara (1970) in the field of soil engineering, should be consulted. All these studies gave specific emphasis to clays and clay minerals. 1.1.19. Clay-organic complexes

Historically, the study of clay-organic complexes has formed one major aspect of clay research, not only in the basic but also in the applied sciences. The number of reports has continued to increase internationally, due partly to the greater diversity of research and partly to the finding of more organic materials capable of forming complexes with clays. In fact, the range of studies now encompasses such divergent topics as the origin of life on the one hand, and water pollution on the other. In the broad sense, clay-organic complexes can be divided into two types : interlayer complexes and peripheral complexes. The former, which are usually observed in expandable clay minerals such as montmorillonite and vermiculite minerals, possess some surprising properties. That is to say, these clay minerals instantaneously form crystals with certain organic molecules at room temperature.and pressure, which may be regarded as hybrid crystals of the inorganic and organic materials. The peripheral complexes may be represented by a schematic model in which the organic materials form bridges among the clay particles. Studies on clay-organic complexes are thus particularly significant in the soil sciences where it is necessary to elucidate the characteristics of associations of organic materials and soil particles. The properties of clay-organic complexes are usually quite different from those of the component clays themselves, so that their use in the chemical industry, soil engineering and agriculture has expanded, as illustrated by the creation of improved or stabilized soils and the product from bentonite known as “Bentone” (Hauser, 1950). The clay-organic complexes reported until recently were all products of reactions between an organic material and clay minerals which have been termed expandable clay minerals. However, since around 1960, it has been known that kaolin minerals, which are regarded as non-expandable clay minerals, also produce clay-organic complexes with organic materials such as urea (Weiss, 1961) formaldehyde or hydrazine (Weiss, Thielepape, Goring, Ritter, and Schafer, 1963). In Japan, one of the foremost problems concerning clay-organic complexes which has been studied is the particular tendency for organic materials (humus) to accumulate in volcanic ash soils. In recent research on fine structures using high resolution electron microscopy, Suito, Arakawa and Yoshida (1969) have observed clear lattice images with organo-montmorillonite flakes (octadodecylammonium complex, etc). Concerning industrial products, “Orben” has been developed by the Shiraishi Industrial Co. by treating montmorillonite with

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16

stea ric acid amide (a non-ionic polar compound) and trimethyloctadecylammonium chloride (Hasegawa, 1958). 1.1.20.

Intersalation

In the period 1956-59, it was noticed that various salts are specifically adsorbed within the interlayer region of halloysite (Weiss, 1956; Wada, 1958, 1959). Wada (1958) found that salts such as cesium chloride, rubidium chloride, and ammonium chloride were adsorbed as monomolecular layers within the interlayer region. In 1961, Wada (1961) discovered that kaolinite can form a complex with potassium acetate, and he later extended these studies further (Wada, 1963, 1965). The experiment was performed by grinding potassium acetate with kaolinite on an agate mortar for about 15-30 min and then allowing the ground material to stand for about 24 hr. Potassium acetate was adsorbed by the repetitive interlayer region as a well-oriented monomolecular layer, resulting in expansion the height of the unit structure from 7 to 14 A. It is surprising that the kaolinite and potassium acetate form crystals instantaneously at room temperature and pressure. When the complex is heated at about IOO’C, the 14 A spacing contracts to about 11.4 A due to the removal of water molecules from the potassium acetate (Fig. 1.2). When the complex is washed with water and then air-dried, the salt layer readily dissolvesin the water causing a contraction of the spacing from 14 to 7 A. Similar complexes are formed with dickite, nacrite, and halloysite (7 A). However, the effects of drying and wetting are not necessarily identical among all these kaolin minerals. Wetting of the halloysite (7 A) complex results in the formation of a 10A spacingcorresponding to that of halIoysite(l0A). The effect of wetting of the nacrite complex is apparently rather complex. The term “intercalation” has been used for phenomena in which there is intrusion of various kinds of materials into the interlayer region of clay minerals. For the purpose of emphasizing this particular process in the case of the for-

f

2.8A

Fig. 1.2. Crystal structural model of the kaolinite-potassium acetate complex (Wada, 1961).

STUDIES ON CLAYS AND CLAY MINERALS

17

mation of salt-clay complexes, the term “intersalation” has been proposed (Andrew, Jackson and Wada, 1960). To date, no data have been reported which indicate that serpentine minerals undergo intersalation.

1.1.21.

Clay catalysts

As stated in section 1.1.1, Kobayashi and his collaborators stressed the importance of the catalytic ability of acid clays, and demonstrated its effectiveness in various organic reactions such as the cracking distillation of fish oils, etc. He also proposed a concept for the origin of petroleum. Recently, Shimoyama and Johns (1971) and Johns and Shimoyama (1972) have discussed the role of clay minerals in the formation of petroleum on the basis of various natural facts and laboratory experiments. It is widely recognized that montmorillonite is gradually transformed into mica in thick strata at increasing burial depth as a result of diagenesis. During the transformation process, the montmorillonite dehydrates and the residual water on the clay surface probably becomes more acidic (Fripiat, Jelli, et al. 1965). On the basis of laboratory experiments, the above authors (Johns and Shimoyama) demonstrated the transformation of fatty acids associated with montmorillonite into n-paraffins through the decarboxylation and cracking of hydrocarbons at 200-300” C . They proposed a mechanism in which the decarboxylation was promoted by Fe, Al, and Mg exposed on the broken edges of the crystallites (which was effective as a Lewis acid) and the cracking of hydrocarbons was promoted by the acidity derived from dehydrated montmorillonite (which acted as a Lowry-Brmsted acid). 1.1.22.

Clay industry

The clay industry is widely developed in Japan, and makes full use of the many important and unique properties of the local clays and clay minerals. The principal uses of the kaolinite and its clay are (1) as raw materials for pottery and refractory products, (2) as fillers or coating materials for paper, and (3) as diluents for rubbers and paints. The pyrophyllite has been used (1) as a raw material for crucibles, refractory bricks and mortar, (2) as a filler and coating material for paper, (3) as a diluent or carrier of pesticides, (4) as a diluent or reinforcing filler for rubber, ( 5 ) as a diluent for paints, cosmetics and chemicals, and (6) as a filling or stiffening agent for various fabrics. The micas, particularly the fine-grained white micas (“sericite”) in Japan, have been used (1) as raw materials for ceramics, (2) as a flux for iron-welding rods, (3) as fillers for synthetic resins and paper, and (4) as admixtures to paints. The bentonite and acid clays are utilized for many purposes. Also, when the latter and their related clays are treated with acids, the useful properties of the clays are particularly improved to give so-called activated clays. Acid clays and activated clays have been used as decolorizing materials, catalysts, adsorbents and desiccants, and in the best cases, as diluents, fillers, admixtures and carriers of various kinds of materials. The principal uses of bentonite are (1) as

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a foundry sand-caking agent, (2) as a pelletizing caking agent, (3) as a component of drilling mud, (4) as a soil improvement agent, and ( 5 ) as a diluent, additive, filler, and carrier of various kinds of materials such as ceramics, medicines, paper, paint, fertilizer, etc. Okino (1967) has performed extensive studies on drilling mud with particular emphasis on its clay mineralogy. Various kinds of by-products are obtained in the process of activation of clays, such as aluminum sulfate, gypsum, silicaalumina gel, and silica-gel (Kuwata, 1957). Both vermiculite and hydrobiotite are utilized after they have been ignited and made to swell. Their properties and light weight are especially conducive to constructional uses such as in heat insulation bricks. The property of fixing ammonia also makes these materials useful in agriculture. Their application for the disposal of radioactive wastes appears promising. Talc has been used in china-ware, paper-clay, as an insectiside carrier, and as an additive for cosmetics and medicines. Serpentine is utilized as a raw material in the preparation of soluble magnesian fertilizers. These are made by crushing and mixing with phosphorus ores, calcinating and fusing at 1400-1 500" C, quenching in water, and finally grinding. Since the soil in Japan is usually relatively acidic, the use of calcium superphosphate fertilizcrs often results in the accumulation of sulfuric acid in the soil. It is then necessary to apply a complete non-sulfuric acid fertilizer in order to build up an adequate phosphorus content and to replenish the magnesia which tends to be washed out by the abundant rainfull. Ishikawa and Tanaka (1959) have performed extensive research on the use of allophane in the petroleum industry. 1.I .23.

Environmental studies

The role of clays in landslides and instances of weak ground has been discussed since ancient times. In Japan, such events tend to be prevalent due to the widespread occurrence of clayey rocks. Throughout geological time, active volcanism has frequently occurred and has produced abundant deposits of glassy tuff, tuffaceous sediments and volcanic ash. Hydrothermal solutions and hot springs resulting from post-volcanic activity have altered these various kinds of rocks to clays. Further, the generally rapid flow of the rivers due to the steep geomorphology, and the active circulation of ground water resulting from the extensive rock fissuring, have favored heavy weathering. Landslide clays, which are found along the slip planes in landslide regions, are diverse depending on the kind of wall rocks. Montmorillonite minerals are usually prevalent in regions of glassy tuffs and tuffaceous sedimentary rocks. The landslide clays in regions of crystalline schists or serpentine rocks are usually composed of such minerals as chlorite, mica, and members of the serpentine group. A considerable number of studies has been made on landslides and weak

STUDIES ON CLAYS A N D CLAY MINERALS

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ground from the viewpoint of the clay mineral assemblages and soil engineering properties of the deposits (e.g. Morimoto, Nakamura, Tsuneshi, Ossaka and Tsunoda, 1967). The name “heavy” clays and soils has been used for certain very disadvantageous clays and soils encountered in land cultivation and road repairs. In general, the materials are dense, have low porosity, and display high plasticity, viscosity, exchange acidity, hydrolytic acidity and/or water content. Mori and Sasaki (1956) have shown that the heavy soil distributed in the Komukai district, Hokkaido, is composed largely of halloysite (10 A) with subordinate amounts of allophane and quartz. Numerous reports have been published in the international literature on the role of clays in soil stabilization. The so-called soil-limeengineering method is one of the main topics. In Japan, the volcanic ash soils are composed largely of halloysite and allophane, and so tend to form weak ground. Ariizumi (1967) has performed fundamental studies on the stabilization of such volcanic ash soils using the soil-lime method. He pointed out that allophane and halloysite (10 A) react with slaked lime to give 2Ca0-Al20,.SiO,.nH,O. They also reported that when gypsum is added with the lime, ettringite (3CaO-A1,O3-3CaS0,. 32H20) is formed, resulting in rapid consolidation. Hayashi of the National Institute for Industrial Health has carried extensive mineralogical studies on dangerous airborne dusts in collaboration with his colleagues at the Institute (Sakabe as leader). Their work has particularly involved the hemolysis and cytotoxity of quartz and asbestos (silicosis and asbestosis). Hayashi (1973) developed an analytical procedure for the quantitative determination of airborne asbestos. This procedure is based on a standard curve prepared by X-analysis of standard samples using high power X-rays. Small amounts of the order of 0.01 mg on a slide glass fiber filter 3.8 cm2 in area, can be detected. 1.1.24.

Societies and publications

The Clay Research Group of Japan (CRGJ) was established in 1958. It produced three kinds of publications : Nendo-Kagaku, (Journal of the Clay Science Society of Japan), Clay Science, and Advance of Clay Science. Nendo-Kagaku was published in Japanese and included review articles, news, and some original articles (with English summaries). Clay Science set out to be an international journal giving original articles principally in English. Advance of Clay Science included the proceedings of the annual general meetings giving the papers read at the meetings in Japanese, together with English summaries. The publication of Advance of Clay Science was discontinued in 1966. In 1964, the Group was reorganized as a Society-the Clay Science Society of Japan (CSSJ), which continues to publish both Nendo-Kagaku and Clay Science.

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1.2. MODES OF OCCURRENCE, MINERAL ASSEMBLAGES AND ORIGINS

The clays and clay minerals of Japan display various modes of occurrence such as in soils, zone of weathering, recent sediments, sedimentary rocks, and hydrothermally altered rocks. Their origin involves weathering, diagenesis, hydrothermal alteration, and combinations of these processes. Crustal movements accompanying igneous activity have frequently occurred in the Japanese Islands from the Paleozoic to the Recent. As a result, clays and clay minerals formed by the hydrothermal alteration ofvarious kinds of rocks, and by the weathering of volcanic glass in rocks or soils, are particularly widespread in Japan. Concerning the clays and clay minerals in Japan, particular attention has been paid to their complicated variability in terms of modes of occurrence, assemblage, areal distribution and origin. This variability results from complicated environmental conditions illustrated in the general sense as follows:(1) original rocks are found to be variable on the small scale, e.g. sedimentary rocks consisting of tuffs, and tuffaceous sediments frequently intercalated by abundant volcanic rock sheets, and (2) such complex rocks have been altered by chemical and physical processes due to a combination of diagenesis, hydrothermal mineralization, and recent volcanic activity. It is necessary first to explain several descriptive terms such as “Green Tuff ”, “Roseki”, “Kuroko”, “Toseki”, “Gaerome clay” and “Kibushi clay”, which appear frequently in the literature on the clays and clay minerals of Japan. These names are applied to particular kinds of ore deposits (Kuroko), rocks (Green Tuff and Toseki), and clays (Roseki, Kibushi and Gaerome). Among them, the Kibushi and Gaerome are described in detail in Chapter 5. Recent advances in the study of the mineralogical and geological properties of the above rocks and clays have revealed that they are very complex and diverse in terms of their clay mineral assemblages, involving various types of interstratifications and unusual (abnormal) species. Indeed, they may be considered the “treasure houses” of clays and clay minerals in Japan, both economically and mineralogically. 1.2.1.

Green tuff

Volcanic activity was particularly violent in the Miocene in Japan, when various volcanic rocks such as basalt, andesite, rhyolite and related pyroclastic rocks such as tuffs and tuff breccias, were formed. These volcanic rocks occur as dykes, sheets and flows. Virtually all of the rocks have assumed a green color due to alteration to green-colored clay minerals. The andesite and basalt are frequently found as propylite or spilitic rocks, respectively. The green-colored rocks are known conventionally as Green Tuff, and they occur as thick beds in strata of the Miocene epoch. The clay minerals in the Green Tuff are usually very complex in terms of their properties, modes of occurrence, mineral assemblages, and origin. They are found as filling materials of amygdales, cavities and fissures, as replacement minerals of phenocrysts of mafic and felsic minerals,

OCCURRENCE, ASSEMBLAGES A N D ORIGINS

21

and as replacement materials of rock groundmass with a glassy texture. Interstratified clay minerals and unusual (abnormal) species are widespread. The clay mineral assemblages are often heterogeneous in samples collected from a small area and, in some instances, even within a single small hand specimen. The process of origin of these minerals is not necessarily local hydrothermal alteration, and is thought to involve local to regional hydrothermal alteration, sedimentation processes, diagenesis, and combinations of these processes. The earlier studies on the “lembergite” (iron-saponite) occurring in Tertiary (Miocene) iron sand beds (Sudo, 1943) (p. 38) and on the iron-rich montmorillonite minerals occurring in Oya-ishi (thick rhyolitic tuffs) (Sudo and Ota, 1952), which is a typical Green Tuff member, have been extended and refined (Sudo, 1954a; Kohyama, Shimoda and Sudo, 1973) (p. 42). These studies are still pertinent to the modern mineralogical work on the Green Tuff. Recently, the importance of carrying out detailed petrological, geological and stratigraphical work on the Green Tuff, in addition to the mineralogical studies, has been felt. Clearly also, work on the precise clay mineralogy of the deposits is essential for understanding the process of origin of the Green Tuff. Work of this nature has begun actively in recent years. Yoshimura (1964) undertook modern studies on the claymineralogy of the Green Tuff including the associated zeolites. Kimbara (1973) investigated in detail the assemblage of clay minerals and zeolites in the Green Tuff occurring in the eastern part of the Tanzawa Mountains, Kanagawa Prefecture. The rocks are composed largely of basalt and its related pyroclastics and occur as thick strata (about 10,000 m in total thickness) surrounding a quartz diorite intruded into the central part of the Mountains. On the basis of its mineral assemblages, the Green Tuff can be subdivided into several metamorphic zones, due to the contact effects of the granodiorite and to diagenetic changes with increasing burial depth. Kimbara considered that the diagenetic changes were dominant in this district, rather than the contact effects of the granodiorite. He summarized the change in clay minerals with increasing (iron-saponite and chlorite)-+ burial depth as follows : (iron saponite)+ (iron-saponite)(magnesian regular or almost regular interstratifications of chlorite and expandable mineral, associated with monomineralic crystals of chlorite)--+ (chlorite) (Fig. 1.3). The interstratifications occur in association with laumontite in the upper horizons, and with prehnite and pumpellyite in the lower ones. There are also some differences in mineralogy, such as in the interstratifications, iron-saponite and chlorite, between the upper and lower horizons, especially as regards DTA curves. The samples referred to here as iron-saponite show an X-ray peak represented by 15 and 1.53 A spacings. However, the samples occurring in the upper horizons are close to montmorillonite (dioctahedral) in respect to their DTA curves: the peak system consists of an endothermic peak between 100-200°C, a broad endothermic peak at about 500°C, a small endothermic peak at about 700°C, and an S-shaped peak.

22

OUTLINE Depth (m)

6000

I

I

5000 1

8

4000 1

I

' 3000

1000

2000

1

I

1

0 I

Heulandite. stilbite

____

c] Analcime Laumontite

j

Prehnite, pumpellyite Montmorillonite

1-1

1Chlorite

Iron-rich saponite (/Mixed-layer

(Il bp=97')

1

IChlorite(1 bp=9O')l

1

0 1 minerals

0

(Hayato ForFig. 1.3. Change in mineral assemblage with increasing burial depth in the Green Tuff mation, Tanzawa Mountains, Kanagawa Prefecture) (Kimbara, 1973). The mixed-layer mineral is essentially ferromagnesian regular or almost regular interstratifications of chlorite and expandable minerals.

The samples occurring in the lower horizons have a peak system which resembles usual iron-saponite or nontronite and consists of an endothermic peak between 100-2OO0C, a broad endothermic peak at about 500"C, and a very broad Sshaped peak or broad exothermic peak in the 800-900°C region. The assignment of the DTA peaks of the iron-saponite has not been fully established: the endothermic peak at about 500°C may be due to a "chloritized effect", as suggested by Mackenzie (1957), or it may be a characteristic peak (p. 42). All the samples termed interstratifications here show X-ray peaks represented by 30 and 1.53 A spacings, and they contain considerable amounts of magnesium and iron. However, the samples occurring in the upper horizons associated with laumontite are generally iron-rich and have a DTA peak system composed of an endothermic peak between 1O0-20O0C, an endothermic peak at about 500"C, and a small exothermic peak in the 800-900°C region. This is close to the system of an iron-rich chlorite in respect to the region between 500-1O0O0C, or close to nontronite in respect to the overall peaks. The samples occurring in the lower horizons associated with prehnite and pumpellyite are relatively magnesium-rich and have a DTA peak system close to that of a magnesium chlorite in respect to the region between 500-1000°C. All the chlorite samples show X-ray peaks represented by 14 and 1.53 A spacings. However, their DTA peaks reveal that they are not free from expandable minerals since weak endothermic peaks occur between 100-200°C. X-ray peaks, which are discernible as due to chlorite in samples associated with iron-saponite and heulandite-stilbite, have disintegrated in the 450-600°C region. The DTA curves of samples having X-ray peaks

OCCURRENCE. ASSEMBLAGES AND ORIGINS

23

due to chlorite associated with interstratifications and laumontite are close to iron-chlorite in respect to their peak system between 500-1000" C: this consists of a sharp endothermic peak between 500-600°C and a weak exothermic peak between 800-900°C. They are iron-rich and mostly of Ib (P = 90") polytype. Samples having the X-ray peaks of chlorite associated with small amounts of interstratifications in the prehnite-pumpellyite zone exhibit a double endothermic peak between 500-600°C and an S-shaped peak between 800-900°C: the intensities are weak compared with magnesium chlorite. The samples are magnesium-rich and mostly of IIb (P = 97") polytype. The above data suggest that each sample is not necessarily monomineralic. It is therefore considered that some samples are composed of a principal clay mineral accompanied by small amounts of another clay mineral which exist as randomly oriented aggregates or as an incorporated body such as an interstratification. Mackenzie (1970) has suggested that "DTA is indeed extremely useful for checking the presence of these interlayers, which may be too few and too randomly interstratified to be detected by X-ray diffraction". However, the above data, in some instances, suggest that the variation in properties of some samples may be due to the unusual (abnormal) properties of some of the clay minerals themselves. Careful examination of X-ray intensities and spacings should also help to ascertain the cause of this variation. In any case, it is very interesting that the samples display variable properties which are correlated with burial depth. The possibility therefore arises that iron-saponite may in fact transform to chlorite through the interstratification, while the chlorite tends to become rich in magnesium with increasing burial depth. 1.2.2. Kzwoko

The submarine volcanic activity occurring in the Miocene gave rise to many metallic and non-metallic ore deposits. Of these, the so-called Kuroko (lit. blackcolored ore) is of great importance. It is composed largely of sphalerite and galena with subordinate amounts of chalcopyrite, pyrite, barite and gypsum. The Kuroko, in places, grades into yellow-colored ore which consists largely of chalcopyrite and pyrite with lesser amounts of sphalerite and galena, and in other places, it grades into siliceous ore composed of quartz with disseminated pyrite and chalcopyrite crystals. The Koroko deposits usually consist of stratiform parts and stockwork parts. The former are massive but generally show zoning of their constituent minerals, while the latter consist of disseminated and network mineralizations distributed in an irregular and funnel-shaped form in rhyolite and its pyroclastics. Those metallic ore deposits which are genetically the same as Koroko deposits but have extremely high proportions of stockwork ore, are usually termed Kuroko-type deposits. The Kuroko deposits are usually accompanied by gypsum ores, as stated above. However, several large gypsum deposits are also found in Japan which are genetically identical to the Kuroko deposits but have only a trace of sulfide

24

OUTLINE

mineralization in and around the ore bodies. These are usually termed Kurokotype gypsum deposits. Concerning the genesis of the Kuroko deposits, it is unanimously agreed among Japanese geologists that they are of submarine exhalative or volcanic-sedimentaryorigin. It is considered that the stockwork type mineralization was probably formed epigenetically from hydrothermal oreforming fluids, while the bedded mineralization occurred syngeneticallyat points where the ore fluids emanated from the submarine surface. As in the case of the Green Tuff, the clays, clay minerals and other alteration products associated with the Kuroko and Kuroko-type deposits are very complex in terms of their properties, modes of occurrence, mineral assemblages and origin. The latter undoubtedly involves sedimentation processes, hydrothermal alteration diagenesis, and combinations of these processes. Iwao, Kishimoto and Takahashi (1954) first performed mineralogical and geological studies on the wall rock alteration of the deposits in the Kosaka mine. Iwao (1956) also studied the wall rock alteration of the Wanibuchi Kurokotype gypsum deposit. Sudo and his collaborators noticed that the clay mineral assemblages of the clay zones enclosing certain stockwork deposits were very close to those of Roseki (see section 1.2.3), comprising chiefly pyrophyllite, kaolinite and diaspore (Sudo and Hayashi, 1955, 1956a, 1957; Sudo, Hayashi and Yokokura, 1958). The close resemblance between the clay mineral assemblages of the Roseki and some stockwork ores was further substantiated by other work. In 1954, a new type of regular interstratification of chlorite (di.-di.-sub-group) and montmorillonite-was discovered in the Kurata Roseki deposit (Sudo, Takahashi and Matsui, 1954) (p. 93). A very similar material was also found in the clay zone developed around a stockwork ore of the Honko ore body of the Kamikita Kuroko mine, Aomori Prefecture (Sudo and Kodama, 1956). The chlorite in these interstratifications is of the di.-tri.-sub-group (p. 93), although it was the sample collected by Hayashi (1961) from the clay zone enclosing the Honko ore body which provided the first evidence in Japan of a monomineralic crystal of dioctahedral chlorite (Hayashi and Oinuma, 1964). Dioctahedral chlorite has also been found in certain Roseki deposits (Henmi and Yamamoto, 1965). Recently, many other clay minerals including interstratified types have been identified in the Kuroko areas, and they will be discussed later in this Chapter and Chapter 8. The wall rock alteration of the Kuroko deposits is described in detail in Chapter 3. 1.2.3. Roseki

Hydrothermal pyrophyllite deposits have Iong been known in many parts of Japan, especially the Chugoku district. The pyrophyllite ore has been termed Roseki ((‘Ro” literally means wax) since it occurs as dense, compact masses having a waxy touch and luster. With the advance of mineralogical studies on Roseki, kaolinite and diaspore were found as accessory minerals in many samples,

OCCURRENCE, ASSEMBLAGES A N D ORIGINS

25

and also as principal constituents in some cases (Table 1.2). The name Roseki is thus currently applied to compact clays composed largely of minerals such as pyrophyllite, kaolinite and diaspore. Recent data for Roseki also indicate the occurrence of many other kinds of accessory minerals such as corundum, mica, andalusite, quartz, boehmite, alunite, aluminian chlorite, regular or almost regular interstratifications of mica and expandable minerals, aluminian regular interstratifications of chlorite and montmorillonite, pyrite, feldspar, etc. TABLE 1.2. Chemical compositions of Roseki and Toseki 1) 2) 3) 4) 5) 6) 7) SiOz 62.20% 65.80% 59.93% 86.26% 51.21% 78.47% 81.48% Ti02 0.18 0.22 A1203 29.93 27.73 30.23 10.44 40.07 14.91 12.42 Fee03 0.11 tr 0.39 0.47 0.10 0.28 0.65 FeO MnO 0.00 MgO 0.06 0.52 0.12 0.33 0.06 tr. 0.14 0.82 1.52 0.03 0.11 0.10 tr. CaO 0.74 0.45 tr. 0.34 0.42 Na2O K2O 0.18 0.08 0.40 2.74 2.10 Ig. loss 6.20 5.01 6.57 2.38 8.51 3.26 3.05 Total 99.16 100.09 100.16 100.12 1-5) Roseki. 1) Mitsuishi, Okayama Prefecture. 2) Shokozan, Hiroshima Prefecture. 3 ) Goto, Nagasaki Prefecture. 4) Mitsuishj, Okayama Prefecture. 5 ) Shokozan, Hiroshima Prefecture. 1-3) Largely composed of pyrophyllite. 4) Siliceous part consists of pyrophyllite and quartz (Matsumoto, 1968). 5 ) Aluminous part consists of pyrophyllite and diaspore. 1)-3), Yoshiki (1958); 4),5), Matsumoto(l968). 6 and 7) Toseki, Amakusa, Kumamoto Prefecture (Takeshi and Shiraki, 1969). 6) 1st class. 7) 4th class. I

Kimizuka (1939) first reported the occurrence of kaolin minerals from the Mitsuishi Roseki deposits. Yoshiki made an extensive study of the microscopic, thermal and chemical properties of Roseki and reported dickite from the Shokozan Roseki (Yoshiki, 1944). The existence of dickite and nacrite was also reported by Iwai, Takeshi and Ossaka (1949) in certain Roseki deposits of the Hokushin area. A new type of regular interstratification of chlorite di.-di.-subgroup) and montmorillonite-was discovered in the Kurata Roseki (Sudo, Takahashi and Matsui, 1954) (p. 93). Henmi and Yamamoto (1965) reported the occurrence of dioctahedral chlorite (probably di.-di.-sub-group) in considerable proportions by weight in the Itaya Roseki, Okayama Prefecture, and suggested the following chemical reaction for its production : boehmite pyrophyllite water-dioctahedral chlorite. Recently Nishiyama, Shimoda, Shimosakaand Kanaoka (1975) have reported the occurrence of a lithium-bearing aluminian regular interstratification of chlorite and montmorillonite from the Tohoo Roseki, Aichi Prefecture, and described it as Li-tosudite.

+

+

26

OUTLINE

1.2.4. Toseki

Toseki is one of the particular rock types which have been used since ancient times in Japan as raw materials for pottery and porcelain. Among the many Toseki deposits, the so-called Amakusa-Toseki, which was discovered in Amakusa, Nagasaki Prefecture, towards the end of the 1600’s, is the largest in scale and the best in.quality. In the general sense, Toseki possesses several characteristics which are favorable for making pottery or porcelain in terms of its workability, vitrification and sintering: it is converted to porcelain if burnt at SK 10 or thereabouts, and contains small amounts of iron and titanium (Table 1.2). Previous studies on Toseki deposits have show that they are usually composed of mica, kaolin minerals, quartz and feldspar in various proportions. For example, the principal constituent minerals of the Amakusa-Toseki (elutriates) are : 5970 %quartz, 15-30 %mica, 7-21 % kaolinite, and 1-3 %feldspar. Theironcontent (Fe203)is 0.28 %, 0.30 %, 0.44 % and 0.65 % in first, second, third and fourth class material, respectively. The favorable characteristics for ceramic use mentioned above may be due in part to the mineral assemblage: the mica and feldspar may serve as a flux. Petrologically, Toseki has been considered to comprise hydrothermally altered rocks derived from rhyolite, lithoidite, perlite or other parent rocks. Recently, Kanaoka (1968) in his extensive study of the mineralogy of Toseki, indicated the following interesting facts. (1) Aluminian regular interstratifications of chlorite and montmorillonite, and regular, almost regular or random interstratifications of mica and expandable minerals, occur in many Roseki deposits in considerable proportions by weight. (2) The polytype of some of the mica in Toseki closely resembles that reported by Shimoda (1970) as 2M2(p. 54). He suggested that the presence of these interstratifications may perhaps have some bearing on the characteristics mentioned above.

1.2.5. Hydrothevinal clay minerals Hydrothermal metallic ore deposits are widely distributed in Japan, and hydrothermal clay minerals are found as gangues in the ores and as alteration products of the wall rocks. Further hydrothermal clay minerals occur as alteration products of various kinds of rocks, and some of these deposits are sufficiently large for exploitation. Studies on hydrothermal clay minerals have often concentrated on clarification of the nature of the wall rock alteration, since this should provide a powerful tool in ore exploration. Lovering (1949) studied the wall rock alteration of the metallic deposits at Tintic, Utah. In Japan, Iwao, Kishimoto and Takahashi (1954) initiated studies on the wall rock alteration of the Kosaka Kuroko deposit. Iwao further extended such work to other deposits such as the Wanibuchi gypsum deposit (Iwao, 1956) and the Ugusu alunite deposit (Iwao, 1963) (Fig. 1.4, A and B). Numerous reports have subsequentlybeen published on the

600 400

200

0 rn

8

Figs. 1.4. Mineral distributions around hydrothermal deposits. A and B. Vertical profiles of the Ugusu silica-alunite deposit, Shizuoka Prefecture (Iwao, 1963). A. Black-Silicified rocks or silica deposits; hatched-Alunitized rocks or alunite deposits; dottedArgillaceous rocks or clays : crosses-Original rocks or basic to intermediate Tertiary volcanics; R-restored surface. B. Distribution of the dominant clay minerals in the clays or clayrocks. Open circles-Kaolin, mostly dickite; double circles-Pyrophyllite; A-Montmorillonite; squuresSericite, illite; solid circles-Mixed layered minerals. C. Lateral mineral variation in amount along the principal adit of the Yonago Roseki deposit, Nagano Prefecture (Sudo, Hayashi, and Shimoda, 1962). D: Diaspore. P: Pyrophyllite. Q: Quartz. K: Kaolinite. The upper figure @,P) shows the total amount of diaspore and pyrophyllite; the blackcolored area at the left-hand side is largely composed of diaspore, and the black-colored area at the right-hand side is largely composed of pyrophyllite.

28

OUTLINE

mineralogy and geology of hydrothermal clay minerals in Japan, and, as overseas, zonal arrangements of clay minerals have often been observed. The principal studies include those on the wall rock alteration of the Nishiazuma mine (sulfur deposit) by Mukaiyama (1954), the copper deposit (veins and replacement deposits) of the Ashio mine by Nakamura (1961), Pb-Zn-Cu veins of the Mikawa mine by Nagasawa (1961), the Yonago mine (pyrophyllite deposit) by Sudo, Hayashi, and Shimoda (1962) (Fig 1.4, C), the gold deposit of the Kasuga mine by Tokunaga (1955), and the Matsukawa geothermal area by Sumi (1968). A geological survey and close inspection of many core specimens from the Matsukawa geothermal area revealed that the Miocene welded dacite tuff and welded andesite tuff, as well as the Pleistocene pyroxene andesite, have undergone complex hydrothermal alteration. It is generally true to say that the alteration zones form a series from the center outwards as follows: (alunite zone)---+(kaolin zone)--+(montmorillonite zone)-(saponite-chlorite zone). It has been reported that regular or almost regular interstratifications of chlorite and montmorillonite, as well as random interstratifications of mica and montmorillonite, tend to occur in the chlorite zone, while almost regular interstratifications of mica and montmorillonite tend to occur in the montmorillonite zone. In general, zonal arrangements of clay minerals are discernible in many alteration areas. Howcver, closer examination often reveals that the alteration features are far more complex than the overall pattern. This suggests that the alteration may not necessarily represent a single stage of alteration but rather overlapping processes of alteration which took place successively or in different stages. 1.2.6. Weathering zones and soils

Due to the widespread occurrence of volcanic ash, pumice beds and glassy tuffs in Japan, studies on the clay minerals of the weathering zones and soils derived from them are particularly important. Seki (1913, 1928) reported the presence of allophane in various volcanic ash soils in Japan, and clarified its general properties. Later, the clay mineralogy of allophane and halloysite was summarized by Ross and Kerr (1934). In about 1954, active work on allophane and related materials was initiated in Japan, as well as in certain other countries such as New Zealand (Sudo, 1954; Fieldes, 1957). Mackenzie (1963) commented that this trend led us back to an older concept, so indicating a reversal of ideas about the kind of principal constituents of clays over the history of clay research. One older concept was that kaolinite (a crystalline mineral) represented the principal constituent mineral of clays in general. Another older concept suggested that clays were largely amorphous. However, with advances in the study of crystal structures, the presence of crystalline materials in clays and soils was greatly emphasized. Then, the study of allophane, a Eon-crystalline or poorly crystalline clay mineral, became active. The present author favoured the concept of Grim (1968) that studies on the non-crystalline and poorly crystalline

OCCURRENCE, ASSEMBLAGES AND ORIGINS

29

clay minerals are of great importance, and that these materials occur not only in volcanic ash soils or clays as principal constituents but also more commonly in general clays and soils than hitherto thought, though in relatively minor amounts. It is even feasible that some of the soil engineering and agricultural properties of clays may be markedly influenced by the presence of small amounts of non-crystalline materials admixed with the clays. Concerning the clay minerals formed by weathering, it appears reasonable to suppose that the crystallites may to some extent grade into poorly crystalline or non-crystalline materials, particularly in the marginal portions. The problem of the weathering of volcanic ash soils is discussed in detail in Chapter 2. 1.2.7. Recent marine sediments Recent marine sediments are usually rich in clays minerals. Many studies have tended to concentrate on the distribution of the clay minerals in terms of their kinds, assemblages and relative amounts. Due to the need to survey many samples, rapid methods for qualitative and quantitative analysis are generally employed. Distribution maps for the clay minerals in marine sediments have been published from the U.S.A., England and U.S.S.R. (e.g. Biscaye, 1965; Griffin, Windom and Goldberg, 1968; Gorbunova, 1966). In Japan, Oinuma and Kobayashi (1966) initiated similar studies, and distribution maps have been prepared from samples collected in the North Pacific, Japan Sea, China Sea, Indian Ocean, and other areas (Fig. 1.5.). They also examined the detailed distribution of the clay minerals in Tokyo Bay, and pointed out that the proportions of different clay minerals are controlled to an appreciable extent by the movements of the sea water: montmorillonite tends to occur in lesser amounts than other clay minerals in areas of more active movement. As for the claymineralogical analysis of sedimentary rocks, they have reported various examples to show differences in clay mineral assemblages between strata of different geological ages, and between different formations of the same age, particularly those between two adjacent horizons in unconformable contact. They suggested that such analysis could help, in some cases, in the stratigraphical subdivision of strata without fossils. These maps have been refined periodically on the basis of additional samples collected and analyzed by these authors and their collaborators (Aoki, Oinuma and Kobayashi, 1975). Aoyagi (1967, 1968, 1969) performed extensive studies on the clay minerals of Tertiary sedimentary rocks found in the oil fields of Japan. Quantitative estimations of the constituent minerals were made on the basis of calibration curves for standard minerals, involving montmorillonite, mica, chlorite, kaolinite, zeolites (analcime and laumontite), cristobalite, quartz, feldspar (albite), calcite, and dolomite. He discussed the relationships between the clay mineral compositions and following factors : lithology, depositional environment, and diagenetic changes. Montmorillonite tended to be dominant in marine sedi-

6d

I 60"

1 80°

1 100"

I 120°

1 140'

I 160"

I 180"

1 160"

I 140"

I 120"

I

looo

Fig. 1.5. Distribution map of clay minerals in Recent marine sediments (less than 2 y) (Aoki, Oinuma and Kobayashi, 1975).

I 80"

OCCURRENCE, ASSEMBLAGES AND ORIGINS

31

I .6 Neogene

s

Tertiary

J

" T i 1 .m

Cretaceous

2

I

I

I

Paleogene

.+

Tertiary

d

I

Cretaceous

Neogene

2 C

Tertiary

$ 1 Cretaceous I

I

I

Fig. 1.6. Variation in mineral compositions of sedimentary rocks of various geological ages. (Abbreviated from the original figure of Aoyagi (1969), selecting the principal mineral constituents.) Mo: Montmorillonite. Mi: Mica. Ch: Chlorite. Q: Quartz. F: Feldspar.

ments, particularly those of neritic or bathyal origin. Kaolinite tended to be dominant in near-shore sedimentary rocks. To the first approximation also the total oil production in various areas composed of Quarternary and Tertiary rocks tended to increase with increasing amount of expandable clay minerals. Aoyagi reported that from the Neogene towards the Paleogene, and to older rocks, montmorillonite tended to decrease in amount, and minerals such as mica, chlorite, and their interstratifications tended to increase. He suggested that this tendency was due to diagenetic changes (Fig. 1.6). 1.2.8. Clay minerals in active volcanic areas Particular attention must be paid to the studies by Ossaka and his collaborators on the clay minerals that occur in association with active volcanoes and hot

32

OUTLINE

springs. Yamada, Iwai and Ossaka (1969) indicated that the mineral assemblages could be well explained according to the pH of the water closely associated with the minerals, i.e. involving the hot spring water and ground water. Opaline silica and aluminum or iron hydrous sulfates are found as alteration products of volcanic rocks which have been subject to attack by strongly acidic hot spring water. Montmorillonite is found as a principal constituent of mud-flows associated with alkaline water. Allophane and halloysite occur in clays associated with ground water that has a pH in the intermediate range. A new submarine volcanic eruption took place near Nishinoshima in about April, 1973. Following the eruption, the sea water became turbid with fine, suspended particles which were yellow to brown in color. Ossaka (1975) reported a DTA curve and X-ray powder diffraction pattern, and gave details of the chemical composition as shown in Table 1.3 and Fig. 1.7 A,B. The exothermic peak in the 200-300°C region may be attributable to non-crystalline iron hydrates. A strongly acidic hot spring water flows out near the seashore of the island of Satsumaiwojima. Close to the exit point, it is transparent in spite of the fact that abundant iron and alumina are dissolved in it. However, the spring water becomes turbid as it flows progressively into the sea. Fine, yellow to brown precipitates are produced probably as a result of chemical interaction with the sea water. Ossaka (1975) analyzed the precipitates chemically, and measured the pH of the sea water associated with them. He found a relationship between the pH values and amounts of Fe203,as shown in Fig. 1.7 C. It was suggested that the pH values of the sea water associated with the precipitates at Nishinoshima were more acidic than the values at Satsumaiwojima. TABLE 1.3. Chemical composition of fine particles suspended in sea water after eruption of the Nishinoshima submarine volcano. (Ossaka, 1975) Dates of collection SiOz Ti02 Ah03 Fez03 MnO MgO CaO NazO KzO Ig. loss Total

Oct. 9, 1973

Mar. 14, 1974

1) 30.20% 22.27 14.93 0.17 0.96 1.85 0.63 27.15

2) 14.97% 0.29 8.56 45.70 1.02 tr 0.50 0.21 28.38

98.16

99.63

_____

The samples were washed in water to remove sea water, and then analyzed chemically. 1) Outside the Bay. 2) Inside the Bay. (Analyst: Y. Ohira.)

CLAYS AND CLAY MINERALS

33 r-!

A

V

1 1

1

200

L

l

I

1

400 600 Temp. (“2)

1

1

800

1

1

1000

I

0

20

40

Fe2O3/(SiO~+Al203+Fe2O3)

60

80 (wt%)

Fig. 1.7. X-ray powder diffraction pattern (A) and DTA curve (B) for fine particles suspended in sea water after the eruption of the Nishinoshima submarine volcano (Ossaka, 1975). (C) Relationship between the amount of iron in precipitates resulting from chemical interaction between the hot spring water and sea water at Satsumaiwojima, and the pH value of the sea water associated with the precipitate (Ossaka, 1975).

1.3. CLAYS AND CLAY MINERALS

1.3.1. ClassiJication

The Nomenclature Committee of the AIPEA (Association Internationale pour 1’Etude des Argiles) has recommended a nomenclature and classification system for clay minerals (Pedro, 1967) which involves only the most general principles for common clay minerals. No firm recommendation is given for a group name to include the montmorillonite minerals, and the nomenclatural decision on a smectite group, or montmorillonite-saponite group is left open. No appropriate short term is recommended to replace the rather lengthy name of the kaoliniie/serpentine group. Further, it is recommended that the name “mica” be used instead of “illite” (Grim, Bray, and Bradley, 1937). The clay minerals dealt with in this book include both common and rare species. As a general principle for the descriptive accounts, the firm recommendations of the AIPEA scheme are followed, e.g. the subdivisions: Type-GroupSub-group. “Type” is defined according to the ratio of tetrahedral to octahedral sheets in one repetitive unit structure. “Group” is defined according to the magnitude of the charge density on the layer surface. “Sub-group” is defined according to the nature of the octahedral sheet. Further detailed points which lie outside the firm recommendations of the AIPEA are decided by the authors’ choice. Thus, the clay minerals discussed in this book may be summarized as follows : (1) Clay minerals having a layered structure based on sheets with 6-member-

34

OUTLINE

ed rings of silica tetrahedra. They are formed by condensation of sheets of silica tetrahedra with sheets of A1 or Mg octahedra. The tetrahedral sheet has no systematic inversion with respect to the site of Si. (A) 2:l Type Pyrophyllite-talc group Di.-sub-group Pyrophyllite Tri.-sub-group Talc Smectite group, or montmorillonite-saponite group (montmorillonite minerals) Di.-sub-group Montmorillonite, beidellite, nontronite Tri.-sub-group Saponite, iron-saponite Vermiculite group (vermiculite minerals) Di.-sub-group Al-interlayer vermiculite Tri.-sub-group Usual Mg-vermiculite, some Al-interlayer vermiculite Mica group (mica minerals or mica clay minerals) Di.-sub-group “Hydromuscovite”, “sericite”, glauconite (mica type), celadonite Tri.-sub-group Brittle mica group (brittle mica minerals) Di.-sub-group Marganite Tri.-sub-group Xanthophyllite Chlorite group (chlorite minerals) Di.-sub-group Donbassite Di.-tri.-sub-group Sudoite, cookeite Tri.-di.-sub-group Tri.-sub-group Various species (B) 1:1 Type Kaolinite-serpentine group Di.-sub-group (kaolin minerals, or kaolinite minerals) Kaolinite, dickite, nacrite, halloysite (7 A), halloysite (10 A) Tri.-sub-group (serpentine minerals) Antigorite, lizardite, chrysotile, 6-layer serpentine (2) Clay minerals with chain-like structures (essentially of 2:l type) and having a systematic inversion in the tetrahedral sheet with repect to the Si-site. Hormite group Sepiolite, palygorskite (3) Miscellaneous (varieties of dubious validity as clay mineral species, or having structures that are not yet defined). So-called garnierite, deweylite, aquacreptite (4) Non-crystalline or poorly crystalline clay minerals. Allophane, imogolite, hisingerite, penwithite

CLAYS AND CLAY MINERALS

35

(5) Interstratified clay minerals Regular type Magnesian regular interstratifications of chlorite and an expandable mineral Corrensite (the expandable mineral is “swelling chlorite” or ranges in the series, “swelling chlorite”+vermiculite--+montmorillonite (more appropriately ferromagnesian saponite) Aluminian regular interstratifications of chlorite and an expandable mineral Tosudite (the expandable mineral is essentially montmorillonite ;the chlorite involves either the di.-di.-subgroup or the di.-tri.-sub-group) Regular interstratifications of talc and saponite Aliettite Aluminian regular interstratifications of mica and an expandable mineral Rectorite Random type (involving diverse degrees of randomness) Notes: Advanced studies have revealed that, in general, the behavior of the expandable mineral tends to be unusual, and the degree of regularity of the layer stacking varies widely between completely regular and completely random. 1.3.2. Pvvoyhyllite and talc

The pyrophyllite-talc group is subdivided into an dioctahedral sub-group consisting of the pyrophyllites, and a trioctahedral sub-group consisting of the talcs. Pyrophyllite occurs as one of the principal clay mineral constituents of socalled Roseki (see Section 1.2.3), which is distributed widely as hydrothermal clay deposits mostly in Southwest Japan and in certain parts of Central and Northeast Japan. Pyrophyllite is also found in association with kaolinite and diaspore as a principal mineral constituent of the clay zones enclosing certain Kuroko ore bodies of the stockwork type (see section 1.2.2) (Sudo and Hayashi, 1955, 1956a, 1957; Sudo, Hayashi and Yokokura, 1958) (p. 93). Kodama (1958) has described the mineralogical properties of the pyrophyllite in Japan, including X-ray powder diffraction data (Table 1.4), chemical compositions (Table 1.5), and a DTA curve (Fig. 1.8). Brindley and Wardle (1970), on the basis of indexing of the X-ray powder diffraction peaks, first clarified that pyrophyllite is divisible into two types according to its crystal system; one is monoclinic and the other, triclinic. The pyrophyllite samples so far described in Japan belong to the monoclinic type. Talc is known to occur in dolomite, serpentine rocks and crystalline schists, mostly in Paleozoic and Mesozoic structural zones. Most of the Japanese talc occurs in serpentine rocks. Among the many deposits, that of Matsumae is the largest. The geology of the area consists mainly of Paleozoic chert and schal-

36

OUTLINE

TABLE 1.4. X-Ray powder diffraction data for pyrophyllite I

001 002 110

iii 02i iii;lii 112

iii 022 003 112

114

ii4 20i ;i30 13i ;200 i4i 20i;131 201 ;113 004 220;220 ii4;041 203;132 227. 222 221 ;I33 024;1% 042 ;024 042 221 222;204 005

043 1343115 etc. 222 224 24i ;025 etc. i5i;310 etc. 1343153 etc. 151 ;24i etc. .

_

____ ~

9.20 4.60 4.42 4.26 4.06 3.764 3.492* 3.454* 3.178 3.068 2.953 2.741* 2.710* 2.569 2.547 2.532 2.416 2.341 2.300 2.215 2.170* 2.152 2.135* 2.116* 2.083 2.059* 2.026 1.998 1.952 1.887 1.841 1.823* 1.812* 1.7439 1.7223 1.6894 1.6674* 1.6529* 1.6327*

**

80 30 100 80 60 5 5 5 20 100 20 3 4 30 30 40 80 10b 5 4 15 15b 2 2 20 25 3b 2
002 004 020 ;110;021 1li ;111;022 006 130;202 200 132 ;204 008 134 222 136;028 136 0,0,10 312 ;150;etc. 134;152 0,0,12;225 060;332 334 156;1,3,10 ;etc. 1,1,!52,0,10 1,3,12;316

9.21 4.58 4.40 4.17 3.08 2.97 2.59 2.55 2.44 2.31 2.17 2.09 2.07 1.895 1.848 1.692 1.650 1.542 1.492 1.475 1.437 1.388

1.373

vs S

ms, b rn,b vs

vw W

mw rn W

W W W

vw

rn W

mw,b W

rnw vw vw

rnw rnw

1) New Zealand. Triclinic system (Brindley and Wardle, 1970). 2) Honami mine, Nagano Prefecture. Monoclinic system; a principal constituent of the Honami Roseki (Kodama, 1958); indices follow the report of Brindley and Wardle (1970). * Not completely resolved. ** Further 21 reflections are recorded in the original text.

CLAYS A N D CLAY MINERALS

37

TABLE 1.5. Chemical composition of pyrophyllite

SiOz Ti02 A1203 Fee03 FeO MnO MgO CaO KzO NazO HzO(+) HzO(-) Pzo5 Total

100

1) 63.57 % 0.04 29.25 0.10 0.12 none 0.37 0.38 tr 0.02 5.66 0.66 tr 100.17

500 Temp. (‘C)

2) 63.79 % 0.47 29.55 0.20 0.14 none 0.33 0.07 tr tr 5.37 0.24 0.02 100.18

3) 62.02%

-

32.24 tr tr none 0.1s 0.40

-

] 6.02 100.86

lo00

Fig. 1.8. DTA curves for pyrophyllite and talc. 1) Honami mine, Nagano Prefecture : pyrophyllite. 2) Korea: talc.

stein, which is intercalacted with dolomite and limestone, plus some associated plutonic igneous rocks and small bodies of serpentine. The talc occurs in irregular or vein-shaped bodies in the serpentine. A DTA curve for a typical sample is shown in Fig. 1.8. 1.3.3. Montmorillonite minerals These minerals belong to the so-called “montmorillonite-saponite group” or “smectite group”, which may be divided into two sub-groups. One is dioctahedral, comprising montmorillonite, nontronite, beidellite, etc., and the other is trioctahedral, comprising saponite, iron-saponite, hectorite, sauconite, etc.

38

OUTLINE

In Japan, as in other countries, the minerals of the montmorillonite-beidellite series occur as the principal clay mineral constituent of acid clays and bentonites which have been altered from rhyolite and rhyolitic glassy tuffs. Their origin involves hydrothermal processes, diagenesis and weathering. Iron-saponite is widely distributed with chlorite minerals and other green-colored minerals in the Green Tuff (see section 1.2.1), and although this mineral has no practical applications in Japan, it does provide considerable mineralogical interest. The montmorillonite minerals are dealt with in detail in Chapter 6. 1.3.4. Historical development of studies on iron-saponite and iron-montmorillonite As mentioned, iron-saponite is widely distributed in the Green Tuff. It occurs in amygdales and fissures in basalt and andesite. It is also found filling fissures in rocks, filling the interspaces of rock and mineral fragments in pyroclastic rocks, and replacing the material of rock fragments, phenocrysts and groundmass. Sudo (1943) studied the mineralogy and geology of the Tertiary iron sand beds in Japan, which occur within the Green Tuff formations. Both the ironsand beds and the tuffaceous sandstones closely associated with them, exhibit a dark green color due to the presence of dark green clay minerals. These cement the sand particles, involving mineral grains such as magnetite, augite, hornblende, plagioclase and quartz, and rock fragments such as volcanic rocks, quartzite and hornfels. It is conspicuous that the dark green color tends to take on a brownish tint on exposure to daylight. The microscopic textures of these rocks are complicated (Fig. 1.9). The dark green-colored material is divisible into two types based on its general appearance : one (so-called Type I) occurs as thin films of uniform thickness surrounding the sand grains and is apparently optically isotropic except for sweeping extinction in some places, and the other (Type 11) occurs as aggregates of fine fibrous crystals or of particles having a spherical or vermicular shape cementing the sand grains. Occasionally, the interspaces of the sand grains are cemented by, and the augite grains replaced by minerals such as calcite, quartz and opaline silica. The green-colored material appears to have greater resistance than the augite grains to replacement by calcite or opal, since dark green material is observed as remnants of ring-like form in the calcite. Usually, the two types, I and 11, lie in contact with a sharp boundary. Although the dark green materials of both types exhibit a family resemblance, it has been problematical as to whether they in fact constitute a single mineral spedies. Great difficulty was encountered in separating Type I from 11, and also in separating distinct parts of Type I1 with different external appearances. The specimens were crushed gently as a whole in a steel mortar and successively passed through a 100-mesh screen. In the powder passing through the screen, the dark green-colored material was somewhat concentrated due to its softness and minute particular state. In order to obtain the dark green-colored material in the purest possible state from the powder, magnetic separation, elutriation,

CLAYS AND CLAY MINERALS

39

Fig. 1.9. Microscopic tcvtures of Tertiary iron sand bcds (Sudo, 1954). M: Magnetite. P: Augitc. S : Opaline silica or volcanic glassy material. Ca: Calcite. Q: Quartz. X : Zircon (?). 1 : Iron-saponite (thin film enclosing mineral grains, Typc I). 11: Iron-saponite (filling material of the interspaces of mineral grains, Type 11). A: Nashino, Miyagi Prcfecture. The interspaces arc mostly filled by iron-saponite of Type 11. Augite grains are partially or entirely replaced by S. B: Nashino, Miyagi Prefecture. The interspaces arc mostly filled by S . C : Saruhashi, Yamanashi Prefecture. The interspaces are mostly filled by calcite which replaces partial augitc grains leaving iron-saponite of Type I behind. Probable calcite occurs rcplacing Type 11. D: Jrisugawa, Gunma Prefecture. The interspaces are filled by quartz replacing Type IT which is left partly behind presumed. Small grains with a high refractive index are supposed to be zircon.

OUTLINE

40

etc. were attempted, and microscopic examinations of the finally prepared powder revealed that it was composed largely of fine fibrous particles with polarization, probably of Type 11. However, it was also found that the material still contained small amounts of plagioclase and quartz. Fortunately, the dark greencolored material is easily decomposed by warm HC1, and chemical analysis of the dissolved parts was next undertaken. Surprisignly, the chemical compositions of the dissolved parts prepared from several samples from different localities were very close to one another. Only the ratio of ferrous to ferric iron varied considerably from sample to sample. This variability arises from different degrees of secondary oxidation of the iron. The amount of ferric iron was then recalculated as ferrous iron. It was found that the chemical composition of the dissolved part (involving &03, FeO, MgO, CaO and water) was very close to that of the alteration products of augite reported in the early days of mineralogy by Lemberg (1877). This resemblance was also confirmed after recalculating all the Fe203as FeO. As regards X-ray powder diffraction data for the dark green mineral, although the work was little developed at that time, there is a strong family resemblance among the dark green mineral, montmorillonite, “garnierite,” and related minerals. Difficulty was also encountered in obtaining Type I in the purest state. However, when rounded grains of cherty rocks surrounded by Type I material were collected and digested in warm HC1 and the dissolved parts were analyzed chemically, the results again resembled the compositions reported by Lemberg. It was presumed therefore that the difference in appearance between Types I and I1 was probably due largely to the degree of minuteness of the crystal flakes, and the dark green-colored mineral under consideration was assigned to the montmorillonite minerals. However, on account of its unusual, complicated chemical composition, the mineral was considered as a possible new species of montmorillonite minerals, and the name “lembergite” was applied to it. Lembergite was later refined by Sudo (1954), with the conclusion that it is correctly assigned to the montmorillonite minerals, but that it may most appropriately be termed “iron-saponite” (Table 1.6, Fig. 1.lo). Recalculating the ferric iron oxides as ferrous oxides, the chemical formula was given as 04 Fei?45

Mgl.5 2 )

62 “0.38)

‘10

(oH)2(Ca/2)0. 46

Miyamoto (1957) reported iron-saponite from Mase, Niigata Prefecture. It occurs in thin films covering the inner walls of amygdales, which are filled by zeolites and calcite, in an altered basalt and its tuff breccia (Table 1.6, Fig. 1.10). The dark green-colored material filling amygdales of basalt at Kokuzo, Nagano Prefecture (Hayashi, Inaba and Sudo, 1961), has a very complicated mineral assemblage composed of montmorillonite minerals (iron-saponite), vermiculite, and their interstratifications. Recently, Kimbara (1973) has reported the wide-

41

CLAYS A N D CLAY MINERALS TABLE 1.6. X-Ray powder diffraction data and chemical composition of iron-saponite 2)

1)

-

d(&

I 40-150

d(h

15.630.8

3)

I 16s

001

15.730.3*

11;02

4.55

10

4.56

7b

13;20

2.62

8

2.63

5vb

d(&

15.2 7.37 4.503 3.140 2.605 2.547 2.440

I 100 6 11 10 9 11 9

2.41 5 5 31;15,24 1.70 33;06 1.53330.001* 10 1.533 8s 1.541 9 1.323 5 EG 16.930.3 17.3 kO.1 Tg FeKa CuKa SiOz 39.68 % 43.98 % 37.52% 0.16 Ti02 0.37 0.03 A1203 3.93 6.30 12.06 Fez03 19.82 7.85 14.34 FeO 1.12 5.32 5.08 MnO 0.19 0.32 0.04 MgO 11.21 18.02 9.12 CaO 2.31 2.78 3.87 1.36 Na2O 0.68 KzO HzO(+) 6.16 9.24 5.02 HzO(-) 15.11 6.24 11.27 Total 99.96 100.21 100.39 Si 3.62 3.42 3.15 AI(1V) 0.38 0.58 0.85 Al(V1) 0.04 0.35 Fe3+ 0.40 Fez+ 1.45** 0.35 1.26** 0.00 Mn 0.02 1.14 Mg 1.52 2.09 0.35 Ca 0.23 0.23 0.22 Na 0.07 K Irisugawa, Gunma Prefecture, occurring in a Tertiary iron sand bed (Sudo, 1954a). 2) Mase, Niigata Prefecture, occurring in amygdales of basalt (Miyamoto, 1957). 3) A sample from the Green Tuff (Hayato Formation), Tanzawa Mountains, Kanagawa Prefecture (Kimbara, 1973). * Spacings calibrated on the basis of the spacings of quartz. ** Chemical composition obtained by recalculating Fez03 as FeO. EG: Treatment with ethylene glycol. Tg: Anticathode.

42

OUTLINE

spread occurrence of iron-saponite in the Green Tuff of the Tanzawa Mountains. The assignment of the DTA peaks of the iron-saponite has not been fully established. An additional small endothermic peak at 500-600” C and also an apparent doubling of dehydroxylation peak may be attributed to a “chloritized effect” as suggebted by Mackenzie (1957) (Fig. 1.10).

I

1

1

I

I

I

I

I

100

200

300

400

500

600

700

800

I 900 1000

Temp. (“C)

Fig. 1.10. DTA curves for iron-saponite. Specimen numbers: see Table 1.6.

Oya-ishi (Oya-stone) represents one of the important building stones in Japan, and is distributed in the Oya district, Tochigi Prefecture. It consists of thick rhyolitic glassy tuffs composed largely of glassy fragments altered to zeolite (clinoptilolite), sporadic celadonite, and occasional montmorillonite on exposed surfaces. The rock is porous and brittle as a whole. It contains numerous volcanic rock fragments with sizes from about 1 to 50 cm. These show the following zonal arrangement: one zone, concentrated with particularly large fragments, alternates regularly and in parallel with a zone without large fragments, so that the alternation forms a bedded structure with clear parallel banding on its transverse surface. The dip of the bedding planes is almost 10” and is parallel to that of the shale underlying the Oya-ishi. The shape of the rock fragments is commonly flat and angular, and each fragment is usually arranged more or less in a horizontal direction, near-parallel to the bedding planes. The rock fragments are massive or exhibit a clear linear texture resembling a wooden block. They contain rare phenocrysts of quartz and plagioclase, of which the latter has the same mineralogical composition (oligoclase to andesine) as the feldspar in the Oya-ishi. The rock fragments are entirely altered to clayey material, which exhibits a deep bluish-green color when unexposed but becomes gray to black in daylight within about 1 hr, and then finally brown within a few weeks. The fragments are thus usually brown in color on exposed surfaces in the field.

CLAYS AND CLAY MINERALS

43

The clay was judged by Sudo and Ota (1952) to be an iron-rich variety of montmorillonite. However, this estimate was later refined by Kohyama, Shimoda and Sudo (1973) to a mixture of two kinds of montmorillonite minerals: iron-bearing montmorillonite-beidellite, and iron-saponite. Microscopically, the clayey fragments exhibit a vesicular texture (Fig. 1.11). The marginal part of each vesicle is pale green, apparently isotropic except for sweeping extinction in places along the edges, and does not show evidence of crystal aggregates (Type I). The core part of each vesicle is dark brown and composed of aggregates of fine fibrous crystal particles (Type 11).

Fig. 1.11. Microscopic texture of clayey altered volcanic rock fragments in Oya-ishi. Left: Parallel nicols. Right: Crossed nicols. (By courtesy of N. Kohyama.)

X-ray diffraction patterns (Table 1.7) of unoxidized and oxidized samples both consist entirely of the peaks of montmorillonite minerals. However, it should be noted that the (06,33) peak usually occurs as a doublet with spacings of 1.53 and 1.50 A, indicating that the samples are composed of both dioctahedral and trioctahedral montmorillonites. It has been confirmed that the b-para-

OUTLINE

44

meters calculated from the spacings of the (06,33) peak on the basis of a monoclinic cell, decrease slightly on oxidation. The DTA curves (Fig. 1.12) of unoxidized and oxidized samples resemble each other closely, showing the peak system of montmorillonite minerals. No doubt, the observed peak system results from an overlapping of the peaks due to the two kinds of mineral species. Bluish-green unoxidized samples consume abundant atmospheric oxygen on oxidation, and the ferrous iron in the samples is easily oxidized in room air on heating up to about 350"C . The Mossbauer effect (Fig. 1.13, Table 1.7) indicates that the discoloration of the samples results from oxidation of iron. Thus, in every respect, the iron in the clay can be said to exist primarily in the ferrous state. The bulk chemical compositions of unoxidized and oxidized samples are

30 100

500

loo0

500

1000

No.9-1

100

Temp. ("C)

Fig. 1.12. DTA and TG curves and the rate of oxidation of ferrous iron inclays altered from volcanic rock fragments in Oya-ishi. The clay is a mixture of iron-bearing montmorillonite-beidelliteand ironsaponite (Kohyama, Shimoda and Sudo, 1973). 9-1) Unoxidized sample. 9-2) Oxidized sample. Broken line: correction curve for increase in weight due to the oxidation of ferrous iron.

CLAYS AND CLAY MINERALS

98

c

94

.. .. . ...... ... .......... ,, ....'..:.'.. ':.... .. . . . . .. . . . . .. .'........... .. . . No.6-1 .: ..... . . . .*

....

q?::.: I

88LI

5 X c

.

....>.. . ....

15nC

I

I

I

I

I

I

.......... ..-' .:...... . .............. ...... ......... . . . No.6-1' ... .... ....'7

.

...

B 0

45

;

;

. .>... . .. ..... . . .

....

1F.A

'"7 I

I

I

....... .........

.

I

I

I

I

I

.

.. ; ,.~.:,>.

.'.

0:.

.. ..;::.'

.'*

.,' '

bi.

No. 6-2

100

. 60

40

-2-1

0

1

2

3

4

5

Velocity (rnm/sec)

Fig. 1.13. Mossbauer spectra for the clay altered from volcanic rock fragments in Oya-ishi (Kohyama, Shimoda and Sudo, 1973). 6-1) Unoxidizedsample. 6-1') Partially oxidized sample. 6-2) Oxidized sample.

shown in Table 1.7. Using EPMA, chemical analysis was performed on the two different parts, Types I and 11. The chemical formula of Type I in the primary state was obtained as (NaO.

5 2 KO. 08 CaO.

26)

(MgO.90

Fei.>.5"2.52)

(si7. 66 "0.

34)020(0H)4r

indicating that the material is an iron-bearing montmorillonite-beidellite. The chemical formula of Type I1 was (NaO.60

KO.

04 CaO.

44)

(M& 04

Fet.:8

"0,

OZ)(si6.

36 "1,

64)020(0H)4,

indicating that the material is an iron-saponite. The chemical formulas of the iron-saponite called "lembergite" and the material from Oya may be compared in their ideal forms as follows; w: Na, K, Ca/2.

46

OUTLINE

TABLE 1.7. Chemical composition, X-ray powder diffraction data and Mossbauer effect of clays altered. from volcanic rock fragments in Oya-ishi, and the b-parameters of the constituent clay minerals in the clays (iron-bearing montmorillonite/beidelfite and iron-saponite) (Kohyama, Shimoda and Sudo, 1973) 6-1)

SiOz

6-2)

Color of powdered sample

brown

2.27

hk

13;20 22;04 31 ;15;24 33 :06

bo

(A)

9.300* 9.030**

brown

2.08

2.09

1::;

30

14.46

37

15b

‘2.59 12.53

1%

5b 8 11 2 3

0.36 0.96

I

brown

I

1.S. (mmisec) 0.35*** 0,s. (mmisec) 0.86*** I

10-2)

d(W)

Q.S. (mmisec) 2.86

~

50.03 % tr 13.94 9.34 2.12 0.28 3.50 1.49 1.50 tr 5.17 12.25 99.62

2.20

1.14 2.52

.

46.77% 0.02 12.47 8.27 3.07 0.20 3.20 1.55 1.50 0.40 5.23 17.92 100.60

I

I

IS. (mmjsec) 1.19

9-2)

32.83 % tr 8.41 0.93 6.75 0.20 2.58 1.38 1.42 0.21 3.46 42.04 100.21

d(A)

1.70 1.536 1.501 1.337 1.293

26 ;40

9-1)

blue

2.20

[4.46

11;02

Fe3’

13.57 9.15 1.56 0.14 4.32 1.99 1.71 0.36 5.17 16.00 100.02

blue

No. of octahedral cations*

Fez+

46.05 %

37.02% 0.02 10.90 0.90 7.61 0.12 3.48 1.61 1.38 0.29 4.86 33.28 101.47

9.216* 9.006**

1.70 1.534 1.503 1.331 1.293

I

9.300* 9.048**

6 4 6 2 2

9.204* 9.018**

6-1) and 9-1) Unoxidized samples. 6-2), 9-2) and 10-2) Oxidized samples. *Iron-saponite. **Iron-bearing montmorillonite/beidellite. ***6-1’ (Fig. 1-13).

d(A)

I

1.70 1.535 1.501 1.330 1.297

4b 4 6 2 2

I

I I

9.210* 9.012**

CLAYS AND CLAY MINERALS

47

,,Al,

Oya-material W l 6 7 (Mg,Fei+) (Si,

67)

O,,(OH),

The data strongly suggest the existence of an iron analog of saponite (an endmember) having the following ideal chemical formula :

In the diagram showing the relationship between the total Fe and Mg content

in the octahedral sheet (per unit structure) and the 6-parameter (Fig. 1.16), the composition of Type I falls within the range of the dioctahedral field, and that of Type I1 within the trioctahedral field. An iron-montmorillonite had been reported earlier by Sudo (1950b) (Table 1.8). This material is generally gray to white in color, but pale green in places, and occurs in association with mica in the clay zone enclosingthe Nisliikannondo ore body (Kuroko) of the Hanaoka mine, Akita Prefecture. Although the pale green color remains unchanged on exposed surfaces in the field, some collected samples tend to acquire a brownish tint on exposure to daylight. Small veinlets or spots of native copper occur in the pale green-colored clay. The occurrence of iron-montmorillonite in Recent marine sediments has been reported by several workers overseas. However, adequate mineralogical data are not available except in the case of the material from the Red Sea termed “ferroan nontronite” by BischofT (1972). Aoki, Kohyama and Sudo (1974) have reported that a montmorillonite mineral is the dominant constituent of a sediment core (total length, 430 cm) collected from Ihe Northeastern Pacific. In the upper half of the core, the ironmontmorillonite occurs in association with mica, kaolinite and chlorite, and occasionally with small amounts of clinoptilolite. Most of the lower half of the core is composed entirely of iron-montmorillonite which occurs as a browncolored clay. The actual site of the core was close to the Clarion Fracture Zone and to the Baja California Seamount Province. The large amounts of ferric iron in the samples could scarcely be removed by treatment with 0.05 N HCl and sodium hydrosulfite, i.e. by the method proposed by Mackenzie (1954) to remove free iron (Table 1.8). Greene-Kelly’s test confirmed that the material examined was montmorillonite. The spacing of the (06,33) peak indicates that it is of the dioctahedral sub-group. The chemical composition (without recalculating the FesOs as FeO) gave a chemical formula in which the tetrahedral sheet is almost entirely occupied by Si, and the total number of octahderal cations is close to 2.00 on the basis of 010(OH)3.These data indicate that the mineral is an ironmontmorillonite. The DTA curves and infrared absorption spectra are included in Fig. 1.14.

TABLE 1.8. Chemical composition and formulas of iron/montmorillonite 1) 46.30%

SiOz Ti02 AbOs Fez03 FeO MnO MgO CaO NazO KzO HzO(+)

2) 44.81% 0.53 7.45 14.29 0.41 1.44 5.73 2.59 0.48 0.86 8.37 12.81 99.77

18.47 6.03 0.45 3.06 2.16 1.03 0.35 6.83 14.50 99.18

HzW-1

2') 51.66% 0.58 8.13 14.08 0.51 0.29 4.21 0.15 1.21 0.71 6.74 10.13 98.40

3) 44.03 1.31 3.25 18.39 0.21 1.49 5.73 2.27

3') 51.72 0.87 7.00 14.41 0.21 0.03 4.70 0.48 1.19 0.70 6.72 10.92 98.95

0.18 0.79 7.81 14.40 99.68

Total Si 3.65 3.97 3.99 Ti 0.03 0.05 AI(1V) 0.35 Al(V1) 1.37 0.74 0.64 Fe3+ 0.36 0.81 0.84 Fez+ 0.03 0.03 0.01 Mn 0.02 Mg 0.36 0.48 0.54 Ca 0.18 0.01 0.04 Na 0.16 0.18 0.18 K 0.04 0.07 0.07 1) Hanaoka mine, Akita Prefecture (Sudo, 1950b) The (060) spacing: 1.51A. 2) and 3) Northeastern Pacific (Aoki, Kohyama and Sudo, 1974). 2 ) and 3') Samples obtained after removal of iron oxides or hydroxides from samples 2) and 3). respectively. The (060) spacing: 1.508 1.509A.

-

I I

100

I

1

l

1

1

I

I

1

500 Temp.

1

('c)

0

I

I

I

I

I

I

I

I

40 30 20 18 16 14 12 10 8 6 Wave number (em-') (X 100)

-

4

Fig. 1.14. DTA curves and infrared absorption spectra for iron-montmorillonite in a core sample taken from the Northeastern Pacific (Aoki, Kohyama and Sudo, 1974). Specimens 2 and 2': see Table 1.8.

i

9.2

-

0

0

4

Fig. 1.15. Estimation of the number of Fe3+ ions in the octahedral sheet from the b-parameter observed for dioctahedral smectite. The data in the figure are from the following sources. Circles: montmorillonit-beidellite (Radoslovich, 1962). Squares: nontronite (Radoslovich, 1962). A: Ironmontmorillonite-beidellite(Kohyama, Shimoda and Sudo, 1973). The arrow indicates the y-value estimated from the b-parameter iron-montmorillonite from the Northeastern pacific. 9.4 0

@

9.3

Montmorillonite-beidellite Nontronite

V V

v v

x Saponite-iron-rich saponite

9.2 '

V

Vermiculite v Biotite A Talc 01

V

nv

D

3

VV

x.p-l x xx

a2

bo(i)

A 3

A 4

i

9.:

9.C

8.c

I

).O

0.5

I

I

I

I

1 .o 1.5 2.0 2.5 Fe +Mg (in octahedral sheet per half unit structure)

I

3.0

Fig. 1.16. Relationship between the b-parameter and total number of Fe and Mg ions. The data in the figure are from the following sources. Montmorillonite-beidellite: Radoslovich (1962), Radoslovich and Norrish (1962), Grim (1968). Nontronite: Radoslovich (1962), Radoslovich and Norrish (1962). Saponite-iron saponite: Radoslovich (1962), Radoslovich and Norrish (1962), Sudo (1954a1, Miyamoto (1957), Midgley and Gross (1956), Quakernoat (1970), Kimbara (unpublish~ddatu). Vermiculite: Radoslovich (1962), Radoslovich and Norrish (1962). Biotite: Radoslovich (1962), Radoslovich and Norrish (1962). Talc: Radoslovich 11962), Radoslovich and Norrish (1962). 1) and 2) Iron-saponite and iron-montmorillonite-beidellite from Oya, respectively (Kohyama, Shimoda and Sudo, 1973). 3) and 4) Iron-montmorillonite from the Northeastern Pacific; samples from which iron oxides and hydroxides had been removed with HCI and sodiurn hydrosulfite; corresponding to samples 2 and 3' in Table 1.8 (Aoki, Koyhama and Sudo, 1974).

OUTLINE

50

Fig. 1.15 shows the relationship between the b-parameter and y-value (ferric iron in the octahedral sheet). The y-value for the present sample read from the diagram agrees well with that obtained from the chemical formula. Fig. 1.16 shows the relationship between the b-parameter and the total amount of Fe and Mg in the octahedral sheet. The plotted points for the present material fall in the range nearer to the trioctahedral field than those of the Oya material, but still within the dioctahedral field. Aoki et al. (1974) suggested that a colloidal mixture of iron, manganese and silica was perhaps originally formed as a result of chemical interaction between sea water and material emanating from submarine hot springs, and that the mixture gradually crystallized out as iron-rich montmorillonite on subsequent diagenesis. Thus, the iron in the material may primarily have been in the ferric state. 1.3.5.

Vermiculite

Mg-vermiculite (trioctahedral vermiculite) occurs in aggregates of green to golden yellow macroscopic flakes that are found in association with talc and chlorite in serpentine rocks which have suffered the contact effects of granites or allied igneous rocks (Table 1.9, Fig. 1.17). Al-interlayer vermiculite occurs in some soils and sedimentary rocks in Japan. Tamura’s method (Tamura, 1958) is well known as the best technique for clarifying the nature of Al-interlayer vermiculite. Sudo, Oinuma and Kobayashi (1961) have studied the Al-interlayer vermiculite occurring in certain cretaceous sedimentary rocks. The samples are composed of very complex clay mineral assemblages involving Al-interlayer vermiculite. Using Tamura’s meTABLE 1.9. Chemical compositions of vermiculite and hydrobiotite

SiO2 Ti02 A1203

Fez03 FeO MnO MgO CaO NazO KzO HzO(+) HzO(-) PZOS Total

33.42 % tr 10.44 3.66 2.34 tr 25.18 4.00 0.02 tr 14.60 6.12 tr

34.1 I % 3.52 16.87 18.84 2.69 0.19

8.04 0.09 0.40 4.06 8.01 3.18 tr

99.78 100.00 1) Vermiculite, Uzumine, Fukushima Prefecture (Shimane, unpublished darn). 2) Hydrobiotite, Onomachi, Fukushima Prefecture (Kato, 1965).

CLAYS AND CLAY MINERALS

51

A

0

E 100

500 Temp. (“C)

1000

I

0

/

I

l

l

500

I

l

l

1

1000

Temp. ( 2 )

Fig. 1.17. A: DTA curves for vermiculite (Shimane, unpublisheddatu). 1) and 2) Uzumine, Fukushima Prefecture. B: DTA, TG and DTG curves for the vermiculite from Uzumine, Fukushima Prefecture (Shimane, unpublished data).

thod, these authors suggested that one sample was composed of Al-interlayer vermiculite and another of Al-interlayer-montmorillonite. The weathered biotite flakes occurring in weathered surface rocks and soils derived from granitic rocks and showing marked exfoliation are known in Japan as “Hiru-ishi”. The material consists of hydrobiotite which is essentially an interstratification of biotite and vermiculite. Kato (1965) performed extensive studies on the weathering products of the granodiorite at Shinshiro City. He pointed out the existence of Al-interlayer vermiculite derived from biotite, which may be called trioctahedral Al-interlayer vermiculite. He also reported that the weathered biotite flakes showed variability with respect to their color, overall mineral assemblage, and chemical composition. With the progression of weathering, the biotite flakes tended to be altered to hydrobiotite (SiO2/AI203 = 3.5-3.7) (Table 1.9), then Al-interlayer vermiculite (trioctahedral) (SiOe/ AI2O3= 3 . 9 , and finally kaolinite and gibbsile. 1.3.6. Mica cla-y minerals

Mica clay minerals may be divided into dioctahedral and trioctahedral species. The Nomenclature Committee of the AIPEA has recommended that the most common name “micas” be used as an inclusive name for these minerals until the nature of so-called “illite” has been clarified. This recommendation can

52

OUTLINE

be adopted for classifying the samples reported in Japan. However, for descriptive purposes, it is necessary to introduce some of the past and present names commonly used in Japan. The term “sericite” (from the Greek for “silky”) has been commonly applied to mica minerals since early days, in mineralogy, petrology and economic geology, and by people attracted by its silky luster as a fine powder. The so-called “sericite” in Japan is all of metamorphic or hydrothermal origin, and until recently it was regarded as a fine-grained (or at least finer than muscovite) Aldioctahedral mica. However, recent studies have revealed that the samples may be divided into two classes: (1) a mica without discernible interstratifications, and (2) an interstratification of mica and rnontmorillonite ranging from random to almost regular types. Thus, broadly speaking, the term “sericite” is at present used as a field name for both (I) and (2), or for (2), only where terms such as “hydromuscovite” or “pure sericite” have occasionally been introduced. Fine-grained white-colored Al-dioctahedral micas have also been reported as principal constituents minerals of Recent sediments or argillaceous sedimentary rocks. However, in Japan, detailed mineralogical studies aimed at describing and identifying these mica minerals have lagged, and they have rather been termed “illite” or occasionally “sedimentary illite”. Recent studies on the mica minerals of argillaceous sediments have revealed that some of them are interstratifications of mica and montmorillonite. Fine-grained white micas in general show some departure from muscovite in terms of their chemical compositions, such as less potassium and more water. Descriptions of “sericite” (i.e. pure sericite) often indicate that the departure lies in the intermediate range between muscovite and “sedimentary illite”. Samples of metamorphic origin and some samples of hydrothermal origin are chemically very close to muscovite. Broadly speaking, the variation in chemical composition of fine-grained micas spreads almost continuously over the range “sedimentary illite” --+ “sericite” -+ muscovite, and the changes do not necessarily result from interstratifications. The mineralogical properties of “sericite” may be summarized as follows. The white micas in crystalline schists have often been called sericite. Such minerals are usually found in polycrystalline aggregates of flakes oriented almost parallel to the flake plane. One specimen from the crystalline schist of the Hitachi mine, Ibaragi Prefecture, is very close to muscovite except for the crystallite sizes. It may represent a macrocrystalline analog of mica clay minerals. Fine-grained white-colored mica clay minerals occur as hydrothermal alteration products of Tertiary rhyolite and its tuffs, and occasionally of granodiorite and shale. They are found in aggregates of powdery crystals having a silky luster, and have been called sericite. The following modes of occurrence are known : (1) large clay deposits without accompanying large metallic mineral deposits : these have in most cases been utilized as a source of mica clay minerals,

CLAYS AND CLAY MINERALS

53

e.g. the sericite (Murakami clay) at Osudo, Niigata Prefecture; (2) a principal clay mineral constituent of clay zones enclosing various kinds of metallic ore deposits such as Kuroko deposits, antimony deposits (the Kanbe mine, Nara Prefecture), and copper deposits (the Ashio mine, Tochigi Prefecture): in some cases, the sericite clay has been used as a source of mica clay minerals after removal of the metallic ore minerals; (3) a principal clay mineral constituent of Toseki; and (4) an accessory mineral of Roseki. Kodama (1957) studied the sericite occurring as a hydrothermal alteration product of granodiorite at Ozawa-mura, Gunma Prefecture (Table 1.lo). The 10 A spacing does not suffer any discernible change in the temperature range up to 1000°C. However, the mineral is chemically distinct from muscovite as follows: Si02/Rz03= 1.3 (1.2 in muscovite), Si02/K20= 9.3 (7.0), R203/K20 = 4.1 (3.2), H20(+) = 0.276 (molar ratio) (0.233). Kodama (1962) studied 14 samples of “sericite” of hydrothermal origin. He termed them “hydromuscovite” and pointed out that they could be divided into three groups with respect to their polytypes: 2M1, lM, and mixtures of them (Tables 1.10 and 1.1 1). He reported out that the departure from muscovite in chemical composition tended to be greater with increasing proportion of 1M type. Although no detailed discussion was made in the original paper as to whether an interstratification was present or not, X-ray powder patterns strongly suggest that no interstratified structure is in fact discernible (at least in the samples of 2M type). Shimoda (1970) reported the mineralogical properties of a fine-grained mica occurring in a hydrothermal alteration product of rhyolite and its related tuffaceous sediments near the Shakanai mine (Kuroko deposit), Akita Prefecture (Table 1.11). He described the mica as hydromuscovite. Although no detailed discussion was made of the presence or absence of an interstratified structure, the reported data strongly suggest that no clearly discernible interstratification could be confirmed. Shimoda pointed out that the X-ray powder diffraction pattern is different from those of the 2M1 and 1M types but rather closely resembled that of the 2M2 type, which is known in lepidolite. Recently, Kanaoka (unpubfisheddata)has pointed out that similar material is often found in Toseki. The DTA curve of the Shakanai material is shown in Fig. 1.18. Shirozu and Higashi (1972) studied many samples of sericite associated with Kuroko deposits, and pointed out that they may be divided into two groups: (1) sericite with no sign of interstratifications (termed by them pure sericite), and (2) interstratifications of mica and montmorillonite. They found that the sericites occurring in the siliceous ore zone or siliceous rocks consisted of pure sericite or contained small amounts of expandable minerals incorporated as interstratifications, while the sericite samples from the clay zone were usually interstratifications of mica and montmorillonite, with small but appreciable amounts of expandable layers. Most of the samples from the black and yellow ore zones tended to be intermediate between the above two (for details, cf. Chapter 3).

OUTLINE

54

TABLE 1.10. Chemical composition of sericite YO(41)

Si02 47.65% Ti02 0.10 A1203 37.03 Fez03 0.01 FeO tr MnO tr MgO 0.04 CaO tr K20 9.02 NazO 0.76 H2O(+) 4.97 HzO(-) 0.73 Pzo5 0.02 Total 100.33

GO

SR(-60)

MY(-M3) MU(-01)

47.24% 0.38 35.04 059

48.21% none 35.40

47.55% n.d. 37.78

0.21 0.16 8.75 1.37 5.52 0.32 99.58

1.53

n.d. 0.36 0.78 8.00 0.46 4.78 0.96 n.d. 100.48

tr n.d. 0.49 0.13 8.18 0.40 4.95 1.30 n.d. 100.78

47.17% none 38.04

SH

SS 48.44% tr 33.84

0.17

0.49

n.d. 0.28 0.36 6.75 0.25 6.22 0.36 n.d. 99.60

tr 0.95 0.11 9.40 0.50 5.42 0.60 99.75

47.14% 0.34 37.09 0.49 0.83 0.57 7.10 0.35 5.18 0.99 0.01 100.09

si

6.17 A1 1.83 A1 3.92

Ti 0.04 Fe3~b0.05 Mg 0.16 Ca 0.08 Na 0.09 K 1.19

Alkali content Quartz KzO Na20 Total impurity 9.02% 9.78 % YO(-01) 0.76 % 2 Mi 0.41 8.34 7.93 MY(-M4) 2 MI 8.46 SR(-60) 8.00 0.46 2 MI-1 M(2:l) (8.32) SR(-Nl7) (0.39) 2 MI-1 M(2:l) (8.71) 5% 8.86 0.43 8.43 MY(-Ml2) 2 MI-1 M(1:l) 8.58 0.40 8.18 MY(-M3) 2 M1-1 M(1:l) 7.93 2 MI-1 M(1:2) 0.37 7.56 MY(-M7) (0.31) (7.74) 10 SR(-N3) 2 M1-1 M(1:2) (7.43) 7.60 0.30 2 M1-1 M(1:2) SR(-N2) 7.30 (7.66) 10 (0.30) SR(-56) 2 MI-1 M(1:2) (7.36) 7.00 0.25 MU(-Ol j 2 M1-1 M(1:2) 6.75 (7.59) 20 (0.96) KA(-60) 1 M (6.60) Y O : Yoji Pass, Gunma Prefecture; a hydrothermal alteration product of granodiorite. GO: Goto Roseki deposit, Nagasaki Prefecture. MY: Kumanodo, Tochigi Prefecture; a hydrothermal alteration product of rhyolite and its tuffs. MY(-M7) and MY(-M10) contain diaspore and quartz as impurities. SR: Shiraishi mine, Tochigi Prefecture; hydrothermal alteration product of rhyolite. MU: Murakami, Nagano Prefecture; a hydrothermal alteration product of andesite. YN: Azumamura, Nagano Prefecture; a hydrothermal alteration product of shale. KA: A sample from the clay zone enclosing the Okunosawa ore body (stratiform type), Kamikita mine (Kuroko deposit), Aomori Prefecture. SS: Seshido mine, Fukushima Prefecture; a hydrothermal alteration product of rhyolite. SH: Shakanai mine, Akita Prefecture; a sample found in association with gypsum and anhydrite in the Kuroko deposit (Shimoda, 1470). Y O (Kodama, 1957). GO and SS (Shimoda,, Sudo and Oinuma, 1969). SH (Shimoda, 1970). Other samples (Kodama, 1962). Bracket: Alkalies contents corrected for quartz impurity. *associated with a sma!l amount of 2Mtype. Specimen

Polymorph

TABLE 1 . 1 1 . X-Ray powder diffrection data for sericite (Kodama, 1962) 2M1 YO(-Ol) Muscovite

hkl 002 004 110 111 022 112 113 023 113 114 006 144

113 025 115 116 200 202 008 131

204 133 22i 22 3

d(i)

10.1 5.05 4.50 4.31 4.12 3.98 3.89 3.74 3.50 3.35 3.21 3.13 3.01 2.88 2.81

I 35 22 12 3 2 5 5 6 10 48 11 5 12 8 6

2.57

13

2.51 2.46

5 4

] 2.38 ] 2.20

5

3b

d(i) I

s m vs w w vw m m

9.99 4.98 4.47 4.29 4.11 3.95 3.87 3.72 3.55 3,475 3.32 3.20 3.1 2.98 2.86 2.78 2.585 2.560

m vs ms vw s m m w vs

2.49 2.46 2.390 2.376 2.245 2.185

w w vw m wb w

vw

2M1+ 1M SR(-60) 2:l Mixture d(i)

I d(A) LO.1 35 10.1 5.06 24 5.03 4.50 10 4.48 4.37 3 4.31 2 4.15 1 4.11 3.98 3.91 5 3.90 5 3.75 3.73 3.67 7 3.66 3.52 10 3.50 3.35 35 3.35 3.20 12 3.20 3.06 10 3.09 3.00 8 2.99 2.94 2 2.87 6 2.86 2.82 5 2.80 2.69 2.57 17 2.57 2.52 4 2.50 2.46 3 2.46 2.44 3 2.39 3 2.38 2.24 2 2.24

1M Muscovite (Radoslovich, 1960) I hkl d(A) I 10.07 s 15 001 11 002 5.00 w-m 12 020 4.487 s 7 iii 4.342 w-m 4.093 w-rn 2 021 10 112 3.647 s 3.482 vvw 40* 003 3.337 s 3.208 ww 11 112 3.0593 s 3 113 2.9211 w 5 023 2.6772 w 2.5875 w-m 130 10 131,203 2.5585 vs(b) 3* 2.4773 vvw 2.4327 w 131 4 132 2.3918 w 2.3509 w 114

2Mz

JSA(-60)

I 80 60 14

4 12 6 6 (2M1) 6(1M) IO(2Mi) 80** 12 (2M1) 8 (1M) 14 (2M1) 12 6 4 22 8 4 8 4

d(A) 10.1 5.01 4.50 4.35 4.11 3.65 3.34 3.08 2.91 2.68 2.57 2.46 2.39

2.2440 w 2** 040 2.2096 vw 220 031,133 2.1901 vvw 2.1020 vw 1 202 2.10 1.997 8 005 2.0766 w-m 1.948 lbr 133 1.9454 vw(b) 1.6856 vvw 2.24

SH hkl 002 004 iii,110*,200* lll*.20i* lli* 202*,112* 113 113,204 114 006 114,204

d(A) 10.25 5.06 4.49 4.31 4.31

I 55 42 60 15 5

3.681 3.520 3.348 3.211

43 33 58 28

115 115*

3.066 2.946

40 15

203 116 311,116*

2.869 2.812 2.583

22 18 90

206*,008* iii* 023,314 117*,208* 22i*,118* 118,221 314*

2.513 2.450 2.426 2.402 2.285 2.252 2.210

10 16 15 14 4 8 7

(Continued)

<

v)

5P

9 4

z

2B

P 9

5:

UI vI

TABLE11.1-Continued

-

2M1 YO(-Ol) Muscovite

-

hkl 206 043 223 00,lO 206 046 138 13,m 321 313 314 13,lO 060

d(A) z 2.13 5

2.006 20 1.977 4 1.736 3 1.653 8 1.602 2 1.558 1 1.527 4 1.501 5

d(A) z 2.14 m 2.13 m 2.05 vw 1.991 s 1.95 w 1.83 vw 1.76 w 1.654 w 1.64 m 1.60 w 1.55 w 1.52 w 1.504 s

2M1+ 1M SR(4O) 2:l Mixture

d(A) I 2.13 3 2.08 4 2.01 17 1.721 1.698 1.669 1.642 1.613 1.585 1.565

2 2 4 3 2 2 1

1.501

8

d(A) I 2.15 6 2.13 4** 2.001 34 1.827 4** 1.733 4 1.663 8 1.650 10 1.595 2 1.527 4 1.509 6 1.501 10

1M Muscovite (Radoslovich, 1960)

KA(-60)

d(A) 1.663 1.634 1.567 1.503

I 4 br. 2 br 2 4

4.25 9 2.13 5 1.824 3 1.544 3

hkl 116 204 060

2Mz

d(A) I hkl 1.6662 w-m 222,316 1.6307 m(vb) 1.5717 w 1.4978 vs(b) 208* 225,118 O,?,lO 228* 420* 131;3,1,10t 422* i.i.ii;228*;2,o.ii* 4 0 , i o* 135:3,1,11t;424* 5i5* 515, 604t, 600* 334*, 426*

SH d(A) I 2.186 7 2.082 20 2.055 15 2.006 30 1.750 3 1.717 10 1.694 15 1.668 15 1.633 8 1.614 8 1.585 8 1.569 5 1.500 30 1.481 4

For sample notations such as YO, SR, KA and SH, see Table 1.10. Bold type: characteristic reflections of the 2M1 an$ IM type:. *Obtained on the basis of the parameters: a = 9.2 A, b = 5.3 A, c = 20. 2 A, /3 = 98.0". **Powder reflections overlapped with strong reflections due to quartz occurring as an impurity; 4.25 A reflection of quartz is omitted. tAdditional indices are possible. 0

C

z

m

CLAYS AND CLAY MINERALS

57

GO

MY

ss

1Eis33 11

SH

12

---

13 100

500 Temp. ("(2)

10001

100

500

1000

Temp. ('C)

Fig. 1.18. DTA curves for micas. I) Sericite from sericite-schist, Hitachi mine, Ibaragi Prefecture. The particle size of the analyzed sample was about 65 p. Q: Quartz. 2) Kamiawashiro, Aichi Prefecture; hydrothermal clay veins in rhyolite. The particle size in the analyzed sample was about 20 p. 3) Chichibu mine, Saitama Prefecture; a sample associated with the lead-zinc veins in a contact metasomatic deposit. 4) Ashio mine, Tochigi Prefecture; hydrothermal alteration product of rhyolite. 5 ) Kamikita mine (Kuroko deposit), Aomori Prefecture; a sample associated with the Tateishi ore body (Stockwork type) of pyrite in rhyolite and its tuffs. 6) and 7)Ashio mine; same as 4). 8) Kamikita mine, Aomori Prefecture; a sample from the clay zone enclosing the Okunosawa ore body (Stratiform type). 9) Kambe mine, Nara Prefecture; a sample associated with antimony veins in hydrothermally altered biotite granite. 10) Mitsuishi (Roseki) deposit, Okayama Prefecture; a sample filling druses in the siliceous parts enclosing the pyrophyllite deposit. 11) and 12) Kanbe mine, Nara Prefecture; same as 9). 13) Osudo, Niigata Prefecture; so-called Murakami clay; a hydrothermal alteration product of rhyolite associated with kaolinite and (in part) pyrophyllite. For GO, YO, etc.: see Table 1.10.

The earlier work by Takahashi and Yagi (1929) on glauconite (Table 1.12) is well known. As in the case of the fine-grained, white-colored mica clay minerals, the abundant information so far collected indicates that the samples of socalled glauconite are quite diverse in their mineralogical properties. Burst (1958) clarified that this diversity involves ordered and disordered, interlayered, and mixed mineral glauconites. The ordered and disordered glauconites are of the non-swelling mica-type, while the interlayered glauconite is of the swelling montmorillonite type. Proper glauconite is probably that designated as ordered glauconite. Burst pointed out that the above variability is related to the degree

58

OUTLINE

TABLE 1.12. Chemical compositions of glauconite and celadonite Glauconite SiO2 Ti02 A1208

Fez03 FeO MnO MgO CaO Na2O K2O

51.55% tr 4.03 22.17 3.54 tr 3.86 0.69 0.55 7.03

H20(+)] 6.62 H2O(-) Pzos 0.03 Total 100.07

hkl

d(A)

001 10.1 002 5.00 020, 110 4.56 iii 4.39 021 4.14 111 112 3.64 022 3.33 003 112 3.09 iij 2.90 023 2.676 130 200,13i 2.59 202, 131 2.487 201, 132 2.402 040,22i 2.265

51.63 % tr 5.01 23.09 2.75 tr 3.71 0.35 0.68 6.75

Celadonite

53.05 %

54.0%

7.04 13.74 1.04

3.2 12.0 3.9

-

-

7.50

4.3 1.7 0.1 3.8

6.25

8.04

7.3

0.02 100.24

-

9.8 100.1

0.22

-

55.99% 0.49 11.13 4.65 7.34 0.20 2.27 0.22 1.30 8.00

50.84% tr. 5.08 19.35 2.28 tr. 6.10 tr. 1.24 8.75

Si Ti AI(IV) AI(VT) Fe3+ Fe2+ Mn Mg Ca Na

K 4.22 3.68 99.49

90.63 Celadonite 2) Z hkl d(A) 203, 132 100 220,041 2.210 10 202, 133 2.149 70 15 005 1.983 133 1.933 17 224 42 311,24i 205, 134 79 204, 135 1.652 50 151 240, 312, 310, 241 15 116 40 ? 1.592 50 060, 33i 1.511 6 330 1.492 46 9

3.99

3.72

0.01 0.93 0.25 0.44 0.01 0.30 0.02 0.18 0.73

0.28 0.16 1.07 0.14 0.67 0.18 0.82

4.48 0.85 98.97 ~~

Z 15 19 21 8

31

10 29 8

3) d(A) I 10.27 100 5.007 7 4.535 33 4.362 24 4.130 18 3.645 3.348 3.3293 3.093 2.902 2.680 2.597 2.576) 2.473 2.400 2.263

d(A)

I

2.208 2.146 1.990 1.959

9 20 14 11

1.660 1.646

20 14

1.589 1.510 1.490

11 31 7

41

55 47 10 31 20 33 4 40 8

Glauconite (Yagi, 1929, 1930, 1932). 1) Hakobuchi Group (Cretaceous), Hokkaido. 2) Masuporo Formation (Miocene), Hokkaido. 3) Recent sediments, Aomori Bay. Celadonite. 1) Shiroishi, Miyagi Prefecture (Sudo, 1951). 2) Oya. Tochigi Prefecture (Kohyama, Shimoda and Sudo, 1971). 3) Taiheizan, Akita Prefecture (Kimbara and Shimoda, 1973).

CLAYS AND CLAY MINERALS

59

of glauconitization. Aoyagi (1965) carried out extensive studies on samples of so-called glauconite from the drilling cores of various oilfields in Japan. He concluded that ordered and disordered glauconites (i.e. of the non-swelling mica-type) are found in only minor amounts, whereas interstratifications of mica-montmorillonite tend to be abundant. He stated that the greater proportion of the samples studied belonged to one of the following types: (1) a micarnontmorillonite interstratified disordered structure showing swelling, (2) a montmorillonite-like highly disordered structure showing swelling, or (3) impure material containing considerable amounts of clay minerals other than glauconite. Celadonite is frequently found in alteration products in Green Tuff, replacing mafic minerals or filling in fissures or amygdales. It is known that celadonite occurs in alteration products of volcanic glass fragments in rhyolitic glassy tuffs. Rarely also, rhyolitic glassy tuffs are themselves entirely altered to celadonite, assuming an overall deep bluish green color (e.g. the bluish-green tuffs near Shiroishi City, Miyagi Prefecture). Rhyolitic glassy tuffs commonly have green-colored spots due to sporadic glass fragments that have been altered to celadonite. The first mineralogical studies were performed on the Shiroishi material (Sudo, 1951a) (Table 1.12, Fig. 1.19). The microscopic texture (Fig. 1.19) is noticeably complex. Celadonite may be divided into two types according to its appearance. (1) Type I : aggregates of submicroscopic particles, in most cases

t

0.1 mm

I

Fig. 1.19. Microscopic texture of celadonite occurring as an alteration product of glass fragments in rhyolitic glassy tuffs at Shiroishi, Miyagi Prefecture (Sudo, 1951a). g: Aggregates of submicroscopic particles filling the interspaces of glass fragments or occurring in the marginal portions of the vesicles (Type I). c: Aggregates of fine fibrous crystals occurring in the central portion of each vesicle (Type

w.

60

OUTLINE

replacing the marginal parts of the vesicles. This type is apparently isotropic except for aggregation-polarization and sweeping extinction in places. Under high power, the apparently isotropic parts exhibit a mottled appearance, indicating the presence of confused aggregates of submicroscopic polarized particles. (2) Type 11: aggregates of bluish green-colored fine fibrous crystals (mean size, 0.01 mm; with a birefringence of 0.01-0.02, positive elongation, and pleochroism as X :yellowish green and Z :bluish green) which occur mostly filling the interspaces of vesicles or in the central part of each vesicle. Under high power, the two types grade into each other. Opal is occasionally found filling the interspaces of glass fragments. The green-colored mineral (celadonite) which is in contact with the opal occurs as aggregates, which are deep green in color and spherical or vermicular in form, or have a concentric texture. Aggregates of submicroscopic green-colored particles of Type I axe also occasionally found filling small amydgales in volcanic rock fragments, replacing plagioclase phenocrysts sporadically, or cutting plagioclase phenocrysts as veinlets. Recently, Kohyama, Shimoda and Sudo (1971) reported the mineralogical properties of the celadonite in Oya-ishi. The material occurs replacing glass fragments

2

T I 100

200

300

400

500

600

700

I 800

1 900

1000

Temp. (%)

Fig. 1.20. DTA curves for celadonite. 1) Shiroishi, Miyagi Prefecture (Sudo, 1951a). 2) Oya, Tochigi Prefecture (Kohyama, Shimoda and Sudo, 1971).

sporadically (Table 1.12; Figs. 1.20, 1.21). Concerning the origin of these celadonites, it is still uncertain whether it may be diagenesis, and/or submarine hot spring action. Kimbara and Shimoda (1973) reported iron-celadonite occurring in amygdales of dolerite at Taiheizan, Akita Prefecture (Table 1.12). Fig. 1.22A shows the relationship between RO and R203 for glauconite and celadonite on the basis of SiO2:2.O0. Although the data sources include rather classical ones, a clear linear relationship is observed. The chemical composi-

4

CLAYS A N D CLAY MINERALS 5

3

8

9

61 10 I

__;L_I

I

r

20

15 I

,

,

,

1 , 1 1 1 1

2 5 ~ I

3600 3530

d 10 3600 3200

1

I0

Wave number (cm-I)

Fig. 1.21. Infrared absorption spectra of celadonite from Oya, Tochigi Prefecture (Kohyama, Shimoda and Sudo, 1971).

0

Celadonite

A Glauconite

1 wq.

& 0.6

A

I

A

A

A

*

'I-

g 0.4

1-"

I 0.5

RO

Fig. 1.22. Diagramatic expressions of the chemical compositions of glauconite and celadonite. A: Figure compiled by Sudo (1949), including some classical data. Sources of data for glauconite: Gruner (19351, Schneider (1927), Hallimond (1922), Maegdefrau and Hofmann (1938), Twenhofel (1939), Yagi (1929,1930,1932a). Sources of data for celadonite: Maegdefrau and Hofmann (1938), Lacroix (1916), Twenhofel (1939), Heddle and Fermore (1926). B: Figure compiled by Kohyama, Shimoda and Sudo (1971), including some recent data. Sources of data for glaluconite: Hendricks and Ross (1951), Burst (1958), Deer, Howie and Zussman (1961), Aida (1968), Porrenga (1968), STM-cards. Sources of data for celadonite: Hendricks and Ross (1951), Sudo (1951), Wise and Eugster (1964), Kohyama, Shimoda and Sudo (1971).

I

62

OUTLINE

tions of celadonite are distributed in the area of RO > R203, while for those of glauconite, RO < &03. Fig. 1.22B shows the relationship between the ratio of octahedralcations as R3+/(R2+ R3+)and tetrahedral R3+. The data sources in this case are rather recent. The two diagrams in Fig. 1.22 suggest that glauconite and celadonite may form a chemical series. As mentioned above, recent studies have revealed that the properties of the so-called glauconite samples are diverse; however, it should be noticed that a rather clear relation exists between some of the chemical components of the two minerals, particularly as shownin Fig. 1.22A. Although the discussion in the classical literature on the nature of glauconite and also of the X-ray data are insufficiently detailed, it is thought that the samples dealt with in these studies may involve proper glauconite, i.e. of the non-swelling mica-type.

+

1.3.7. Brittle mica minerals Brittle mica minerals are usually found as macrocrystalline flakes. Studies on them are significant in connection with the structure of clays belonging to the phyllosilicgat-group.-The structure of brittle micas has been described by Takeuchi (1965). Harada, Kodama and Sudo (1965) reported the properties of xanthophyllite ftom the Chichibu mine, Saitama Prefecture. This mine involves contact metasomatic deposits of iron and copper. The xanthophyllite is found as beautiful crystals, 1-8 mm in width and 1-2 mm in thickness, associated with vesuvianite and other skarn minerals in crystalline Permian limestone lying in contact with intrusive quartz-diorite. Data on the X-ray powder diffraction pattern, chemical composition, infrared absorption spectra, and thermal transformation of this material were given. 1.3.8.

Chlorite minerals

Chlorite minerals form a group of hydrous silicates containing elements such as magnesium, ferric and ferrous iron, aluminum, manganese, chromium and lithium. Studies on them date back to the remote past. The numerous data given in general texts are concerned mostly with the Mg-, Fey-or Mg-Fe-rich minerals, i.e. -the trioctahedral sub-group, although data for dioctahedral chlorites have recently become available. In Japan, earlier data have been given for the following species :the penninite and kammererjte occurring in association with chromite deposits in serpentine (Sasamoto, 1895), delessite occurring in the Izumi Sandstone (Yagi, 1932b),manganiferous thuringite from Ichinokoshi, Tateyama, Toyama Prefecture, and manganiferous chamosite (14 A-type) in copper-quartz veins of the Arakawa mine, Akita Prefecture (Sudo, 1943). Recently, Shiroza has added much to our knowledge of the crystal structure, polyiypes and crystalchemical properties of chlorite minerals. The existence of dioctahedral chlorite was confirmed in Japan as monomineralic state or in a new type of interstratified miner al-aluminian regular interstratification of chlorite and montmorillonite-

CLAYS AND CLAY MINERALS

63

found in Roseki and Kuroko deposits, (Sudo, Takahashi and Matsui, 1954; Hayashi and Oinuma, 1964). Details are given in Chapter 7. 1.3.9. Kaolin minerals

The kaolinite-serpentine group may be divided into two sub-groups : the dioctahedral sub-group (kaolinites) and trioctahedral sub-group (serpentines). The former comprises kaolinite, dickite, nacrite, halloysite (10 A) and halloysite (7 A). Details are given in Chapter 5. 1.3.10.

Serpentine minerals

The chemical compositions of the serpentine minerals tend to approach a constant ideal with 3Mg playing the role of the 2A1 in kaolin minerals. The principal species known to date are: chrysotile (ortho, clino, and para), lizardite (1 -layer ortho-serpentine), 6-layer ortho-serpentine and antigorite (Zussman, Brindley and Comer, 1957). Differentiation among these minerals is made essentially on the basis of crystal structure analysis of single crystals. The morphology of the crystallites in the dispersed state, as revealed by electron microscopy, varies between tubular, platy, lath-shaped forms, coarse and fine. Chrysotile is generally found as tubes, and the other serpentine minerals usually consist of equidimensional flake-shaped or elongate lath-shaped units. The principal X-ray powder reflections are common among the serpentine mineals, although some finer points do aid the differentiation of different species in some cases. The minerals commonly exist as intimate mixtures of two or more species or as mixtures with other impurities, however, so that it is often difficult to identify each species from the rather confused X-ray powder patterns. Tomisaka and Kato (1963) studied 20 samples of serpentine minerals in Japan by means of electron microscopy, electron diffraction and chemical analysis (Table 1.13). They concluded that the samples were mostly mixtures of two or three mineral species. They gave a general chemical formula for serpentine minerals as follows :

They deduced several broad tendencies for the relationship between polytype and chemical composition as expressed by the x-,z-, and y-values, where the yvalue was defined as Mg/(Fe2+ Mg)( ”/,). The z-values were noticeably larger in chrysotile than the other minerals. The y-values tended to increase from chrysotile to antigorite through lizardite. The x-values of chrysotile were less than the other minerals. Shimoda (1967) has reported the mineralogical properties and kinetics of dehydration of certain serpentine minerals, as shown in Tables 1.13, 1.14, and Figs. 1.23, 1.24.

+

TABLE 1.13. Chemical composition of serpentine minerals 1) 2) 3) 4) 5) 6) SiOz 40.85% 43.84% 39.10% 46.91% 40.67% 43.15% Ti02 tr tr Ah03 1.71 2.23 0.18 0.61 0.83 7.49 Fez03 2.68 3.72 1.99 1.72 2.90 0.40 FeO 4.57 0.43 MnO 0.08 0.07 0.02 0.11 tr 35.82 38.16 38.10 34.50 39.43 32.39 MgO CaO 0.09 tr 0.06 0.15 0.76 Na20 0.11 0.04 0.14 0.02 0.08 KzO 0.02 0.07 H2O(+) 12.31 12.28 15.60 13.76 13.36 13.77 HzO(-) 1.02 0.36 5.16 2.45 1.78 2.54 Total 99.13 100.85 100.64 100.01 99.44 100.52 1) Kodo, Yamaguchi Prefecture; antigorite. 2) Komori, Kyoto; antigorite. 3) Maruo, Yama. guchi Prefecture; ortho-chrysotile with small amounts of lizardite. 4) Sambagawa, Gunma P r o fecture; chrysotile. 5) Ogose, Saitama Prefecture; 6-layer ortho-serpentine. 6) Nagatoro, Saitama Prefecture; aluminian serpentine. 1-3) Tomisaka and Kato (1963). 4-6) Shimoda (1967).

1

2

k 100

500

900

Temp. ( 2 )

Fig. 1.23. DTA and TG curves for serpentine minerals (Shimoda, 1967). 1) Chrysotile, Sanbagawa, Gunma Prefecture. 2) Aluminian serpentine, Nagatoro, Saitama Prefecture.

CLAYS AND CLAY MINERALS

65

TABLE 1.14. Dehydration data for serpentine minerals Temp.( O C)

Mineral Chrysotile (Sambagawa) Aluminian serpentine Six-layer ortho-serpentine Antigorite

I

J

I

700

00 Temp. (%)

I K

6X 10-4d(deg-1)

1

36.9 54.5 67.6 54.0 69.9

I

I900

AH

E

n

630 0.4 650 0.6 668 0.5 720 1 .o I745 0.5 Temp. : Peak temp. on DTA curves. n: Order of reaction. E: Activation energy (kcal/rnol). AH: Heat of dehydration (kcal/rnol of dehydrated water).

500

13.3 14.0 16.0 16.7

I

I

700

1

900

Temp.(%)

6 x 1O-'

-Io (deg-I)

Fig. 1.24. DTA, TG and DTG curves and the kinetics of dehydration of serpentine minerals (Shimoda, 1967). K: Antigorite, Kornori, Kyoto. 0: 6-layer serpentine, Ogose, Saitama Prefecture.

66

0UTLIN E

1.3.11. Sepiolite and palygorskite

Sepiolite was first described in Japan by Muraoka, Minato and Takano (1958). It occurs in veinlets or small masses in the serpentine rocks which form the wall rocks of the chromite deposit at Yoshikawa-mura, Fukuoka Prefecture (Table 1.15). Imai, Otsuka and Nakamura (1967) later reported sepiolite from the Akatani mine, Niigata Prefecture, which is a hydrothermal replacement deposit of hematite. The sepiolite occurs in veinlets cutting across crystalline limestone and altered skarn minerals. Imai, Otsuka, Nakamura and Inoue (1 966) described sepiolite from the Karasawa mine, Kuzu, Tochigi Prefecture, which involves limestone and dolomite deposits of the Chichibu Paleozoic system. The sepiolite occurs as veins along faults within the limestone. Recently, Hoe and Hayashi (1975) have reported a new occurrence of ferriferous sepiolite from Akan-cho, eastern Hokkaido. The mineral is found in dyke form, 30-150 cm in width, cutting the Nuibetsu Formation (Oligocene) (Tables 1.15, 1.16). These authors stated that the sepiolite is a hydrothermal alteration product of plagioclase porphyrite intruded into tuffaceous sandstone of Paleogene age. Iron-sepiolite described by Shimosaka, Kawano, and Sudo (1976) occurs as cavity-fillings associated with talc, and serpentine minerals in recrystallized dolomite (Paleozoic formation) of the Kasuga mine, Gifu Prefecture. Palygorskite was first described in Japan by Minato (1966) from the Hanezuru mine, Kuzu area, Tochigi Prefecture (Tables 1.15, 1.16). It occurs in leather-like aggregates, several millimeters in thickness, on weathered surfaces of dolomite. Minato, Imai and Otsuka (1969) later reported another occurrence of palygorskite from the Ogano mine, Kuzu area. It occurs in veins along the Ogano Fault No. 10 cutting across carbonate beds. It is known that sepiolite dehydrates in two steps (I and 11) in the 250-650°C region. Recently, Nagata, Shimoda and Sudo (1974), using a sample from the Kuzu area, studied the dehydration behavior in detail on the basis of X-ray powder diffraction data (Table 1.16), DTA and TG curves (Fig. 1.25), infrared absorption spectra (Fig. 1.26), kinetic data on dehydration (Table 1.17), etc. On the basis of indexing X-ray powder diffraction patterns of the untreated sample and samples heated up to about lOOO"C, the effects of heat on the lattice parameters were made clear. The above authors confirmed the existence of discontinuous changes between the two steps of dehydration with respect to the energy of dehydration and lattice parameters. They concluded that the structural states of the two steps may exist in the form of two different dehydration phases, as shown schematically in Fig. 1.27.

67

CLAYS A N D CLAY MINERALS

TABLE 1.15. Chemical compositions of sepiolite and palygorskite Palygorskite

Seuiolite 52.85 %

Ti02 A1203 Fez03 FeO MnO MgO NiO CUO CaO NazO KzO HzO( +) H20(-) Pzo5

coz

tr 0.03 0.42 none 22.03 0.06 tr tr

}

1.03 0.04 0.01 <0.01

23.74

0.51

0.12 9.99 18.49

9.04 12.67

-

3) 50.74% 0.03 2.87 9.02 1.64 0.79 13.20

0.79 1.99 2.38 8.05 8.55 -

-

4)

52.15% 0.05 0.12 8.23 1.66 0.10 17.99

0.74 0.18 0.06 9.01 9.08 t0.01 0.81 100.18

(96.71)

99.97 7.83

-

7.85 0.03 0.12 1.72 0.07

1.75* 0.02 6.05

2.10

2.04

0.23

0.36

100.05

Si Ti Ai (IV) Al (VI) Fe3+ Fez+ Mn Mg Ni cu Ca Na K

12.0

11.79

11.48 0.01 0.51 0.26 1.54 0.30 0.15 4.45

12.01 0.01 0.03

0

30.0 6.0 7.5 10.2

0.19 0.77 0.69 32

0.06 0.08 0.02 32

H H2 0 OH

0.1

8.0

7.89

32

1.49

11.30 8.70

99.89

0.21 0.06 0.01

-

0.01 9.69

2) 53.75 none 10.23 1.83 0.26 none 9.39

2.29 tr 0.02 12.04 10.16

100.56

Total

53.81 0.21 10.85 0.65

-

-

-

21

-

-

0.17 1.58 0.19 0.03

21

Sepiolite. 1) Yoshikawa-mura, Fukouka Prefecture (Muraoka, Minato, Takano and Okamoto, 1958). 2) Karasawa mine, Kuzu, Tochigi Prefecture (Imai, Otsuka, Nakamura and Inoue, 1966). 3) Ferriferous sepiolite, Akan-cho, Hokkaido (Hoe and Hayashi, 1975). 4) rron-sepiolite from the Kasuga mine, Gifu Prefecture (Shimosaka, Kawano and Sudo,-1976). Refractive indices: a = 1.508, y = 1.525. Lattice parameters: a0 = 13.74 A, bo = 26.97 A, co= 5.28 A. The structural formula was calculated by converting ferric iron into ferrous iron. The authors suggested that the sample was primarily a ferrous iron-sepiolite. Palygorskite. 1) Hanezuru, Kuzu, Tochigi Prefecture (Minato, 1966). 2) Ogano, Kuzu, Tochigi Prefecture (Minato, Imai and Otsuka, 1969). The chemical formula of sepiolite-1) is based on the Nagy-Bradley model, and the others on the Brauner-Preisinger model.

OUTLINE

68 TABLE 1.16. X-Ray powder diffraction data for sepiolite and palygorskite

h k I

10 3 0 4 0 11 5 0 3 1 1 3 1 2 2 1 2 3 1 2 6 0 24 1 0 8 0 33 1 26 1 4 11 4 6 0 5 10 19 1 1 1 0 0 1 0

I 1

d(A) 12.23 7.531 6.732 5.036 4.515 4.324 3.997 3.759 3.542 3.360 3.198 3.054 2.821 2.690 2.623 2.565

1) I h k I d(A) I vs 3 8 1 2.405 40 450 62

253 91 85 3 10 1 85 4 0 2 20 4 6 2 6 81 1006 0 2 35 0,12,2 180 6 1 2 1006 9 1 40 6 6 2

:]

2.449

2 9 1

]

'8

hkl 110

200;040

2) d(A) I khl d(A) 12.26A 100 110 10.57 200 6.41 7.55 5 130 6.43 040 4.49 6.70 2 4.27 5.03 2 310 4.17

3) I khl d(W) 100 510 2.547 20 2.520 18 37 530 2.378 2.302 17 080 2.252 23 12 600 2.166 2.125 550 2.097

8 10 8

3.735

3.30 400 3.23 9 3.20

11 1.913 31 480 1.875 32 390 1.805

6 4 3

3.531

1

18 660 1.766

5

21 1.726 7 1.673 6 800 1.614

3 6 3

10 680 1.564

3

2.124 20 2.072 65 1.897 15 1.759

060

4.480

8 240 3.69

1,700 30

131

4.307

8 150

330

4.000

1

150

1.594 60 1.5891

3.361 3.195 3.056

14 420 3.04 2,796 7 2.901

1

2.828 2.785 2.696 2.619 2.561 -

3.11

2.684 440 2.597

21

2 2 5 3 6

1) Sepiolite, Kuzu, Tochigi Prefecture (Nagata, Shimoda and Sudo, 1974). 2) Ferriferous sepiolite (Hoe and Hayashi, 1975). 3) Palygorskite, Ogano mine, Kuzu, Tochigi Prefecture (Minato, Imai and Otsuka, 1969).

TABLE 1.17. Dehydration kinetics of sepiolite (Nagata, Shimoda and Sudo, 1974)

n

300-550

n: Order of reaction. E: Energy of reaction.

2 3 3

241 260

65 3,15,1 75 6,12,0 1,580 4,11,2 080 408 41 1 83} 1.550 30 331 7 12 4,12,2 261 2 831 1.519 20 0 93 70 9 3 1 1.415 55 1.350 15 081 1.299 75 421 0,10,0;510 441;281 530 112;371;191 132

Original sepiolite

I 26 22

Step I1 (200400°C) Step I11 (4W600"C) Step 111 (400-600°C)

1.3 1.3 1.3

E (kcaljmol) 21.9 31.3 31.1

CLAYS A N D CLAY MINERALS

69

J 100

300

700

500

900

Temp. (‘C)

B 10%

1

I

1

200

l

l

400

I

l

600

1

1

800

Temp. (Oc)

I.3.12.

I

I I 1co3

Fig. 1.25.A. DTA and TG curves for untreated and heated sepiolite (Nagata, Shimoda and Sudo, 1974). 300-120: a sample heated at 300°C for 120 hr, etc. B. DTA, TG, and DTG curves of ironsepiolite from the Kasuga mine, Gifu Prefecture (Shimosaka, Kawano and Sudo, 1976). Sample weight: 17.6 mg in DTA, and 119.5 mg in TG and DTG.

‘%arnierite”

In Japan, “garnierite” is known to occur in association with nickel ore deposits in serpentine rocks; the ore mineral is represented by millerite (Sudo and Anzai, 1942). “Garnierite” is found in massive aggregatesoften replacing millerite crystals, such as at the Miyagawamine, Nagano Prefecture,and Wakayama mine, Oita Prefecture. An interesting occurrence of “garnierite” is known in the case of the hard green oolites or incrustations which are found in small druses in magnesite masses at the Wakayama mine. Microscopically, the material is composed largely of oolitic opal covered with thin films of “garnierite”. Moreover, at the center of each oolite, there are usually acicular crystals of millerite which are partially replaced by opal or “garnierite”. Kato (1961) studied 14 sam-

OUTLINE

70

Elatural

300-1 20 300- 250

400-1 20 400- 200

500-1 20 600-1 20

1409

1200

1000 800 600 Wave number(cm-')

400

Fig. 1.26. Infrared absorption spectra of untreated and heated sepiolite (Nagata, Shimoda and Sudo, 1974). 300-120, etc : see Fig. 1.25. Sepiolite anhydride

Natural sepiolite

I

Enstatite

,

Fig. 1.27. Structural models for sepiolite and its dehydrated phases (Nagata, Shimoda and Sudo, 1974).

ples from New Caledonia on the basis of X-ray powder diffraction, electron microscopy, electron diffraction, spectrochemical analysis, infrared absorption spectra, DTA curves and heat treatment (Table 1.18, Fig. 1.28). From the data obtained, the samples were grouped into the following types : 7 8,antigorite-type

CLAYS AND CLAY MINERALS

71

TABLE 1.18. So-called “garnierite” from New Caledonia (Kato, 1961) Locality

Under the electron-microscope Rounded thin plates Poya Rounded thin plates 2) Tubes and fine plates Thin plates and some tubes Poum 5) Thin plates and some tubes Fine plates Pita Tubes and fine plates 8) Thin and fine plates and tubes 9) Theodie Fine plates Thin and fine plates Thio Rounded thin plates 12) Rounded thin and fine plates 13) Les Carrieres Rounded thin plates 14) Nakety Thin plates, lath, some tubes

”1

Products on ignition E+F

E

F

F

SiOz A1203

Chemical composition

RO*

HzO(+)

Fez03 NiO MgO KzO NazO HzO(+) HzO(-) Total

Poum

1)

4)

*Molecular ratio calculated on the basis of SiO :4.00. F, Forsterite. Q, Quartz.

Thio

Pita 5)

39.39% 37.91% 37.40% 17.51 1.99 3.29 0.58 1.85 4.50 4.21 6.39 6.05 21.78 30.55 29.11 0.11 0.13 0.07 0.03 0.03 0.25 11.86 11.72 12.07 4.76 10.09 7.60 100.19 100.64 100.40 5.35 4.13

+

(Q) F E+F F F F

ii;}

Poya

+ F + (Q) F F + 03

5.14 4.30

8)

12)

Identified minerals chlorite antigorite chrysotile, talc antigorite antigorite talc serpentine, talc serpentine, talc talc talc, antigorite talc, chlorite talc, antigorite antigorite serpentine, talc

Les Nakety Carrieres 13)

39.70% 35.75% 26.52% 2.14 3.09 1.21 0.14 2.91 0.36 30.88 36.20 49.45 7.61 3.08 5.10 0.11 0.02 0.04 tr. 0.07 0.04 7.93 9.02 10.80 11.34 10.38 5.99 99.85 100.52 99.51 3.68 2.69

3.76 3.35

7.82 5.94

14) 39.15% 2.68 0.54 34.92 5.15 0.03 0.05 11.45 5.81 99.79 3.69 3.95

**E, Enstatite.

(platy), 10-1 1 A talc-type, 7 A chrysotile-type, and 14 A chlorite-type material. Kato pointed out that RO tends to increase with increasing HzO(+) (Fig. 1.29). The plotted points are distributed in an area above the straight line which is made by connecting the ratios, H&l(+)/RO, obtained from the ideal formulas of talc and serpentine. Thereby the present speciemens contain HzO(+) in excess, a part of which may be attributable to the presence of zeolitic water as judged from TG curves. Recently, nickel-containing layer silicates have been studied in detail by

OUTLINE

72 A

B 1

1

6

9

9

6

10

10

11

11

14

3 2

7 14

9

7 12

4 4 F

s 13

1:

Fig. 1.28. X-ray powder diffraction patterns (A) and infrared absorption spectra (B) of samples of so-called “garnierite” (Kato, 1961). SampIe numbers: see Table 1.18. Q: Quartz.

Brindley and his collaborators (Brindley and Hang, 1973; Ueda, Hang and Brindley, 1973; Hang and Brindley, 1973). They recommended the following classification : 10 A talc-like type involving kerolite (Mg end-member) and pimelite (Ni end-member), and 7 A serpentine-like type involving the following series: chrysotile-pecoraite, lizardite-nepouite, and antigorite. 1.3.13. Deweylite

Deweylite is a hydrous magnesium silicate occurring as a fissure-filling or incrustation occasionally associated with chromite in serpentine (Sudo and Minato, 1949; Kato and Minato, 1960). Kato and Minato performed mineralogical studies on several samples (Table 1.19, Fig. 1.30) involving nickel-bearing deweylite from Hirose, Tottori Prefec-

CLAYS AND CLAY MINERALS

73

0

A 0 0

A

Fig. 1.29. Relationship between RO and HzO(+) in samples of so-called “garnierite” and deweylite (Sioz:4.00)(Kato, 1961). 0 : Carnierite (Kato, 1961). A : Carnierite, as reported by other authors. 0: Deweylite.

ture. The X-ray powder diffraction patterns are rather diverse. However, based on the reflections having medium to strong intensities, they may be grouped into 7 8, and 10 8,types; some peaks (weak and broad) are also observed in the 1017 8, region. The 7 A peak disappears in the 700-800°C region, whereas the 10 8, peak does not. As in the case of “garnierite”, RO tends to increase with increasing H20(+). Rehydration is observed after heating at about 300°C. Then, the HzO(+), at least in part, may exist as zeolitic water. (Fig. 1.29).

OUTLINE

74

TABLE 1.19. Chemical composition and X-ray powder diffraction data for deweylite (Kato and Minato, 1960)

A1203

Fee03 FeO MgO MnO NiO CaO NazO KzO HzO(+) H2O(-) Total Refractive index Specific gravity SiOz = 4.00 Rz03 RO H2;0(+) HzO(-)

d(A) 17 14 12 11 10 8.0 7.4

32.48 none n.d. 1.10 0.02 0.13 9.14 10.14 100.84 1.49

2.17

2.19

0.11 4.52 2.03 1.55

0.14 4.37 2.73 3.55

Z W W

ni

m

d(A) 17 15 12 11

Z W

W

S

3.8 3.7 3.6 3.5

W

s-m

m W W

8.2 7.8 7.4 5.0 4.6 4.5 4.4 4.0 3.8 3.7 3.4

m

-

1.2 -

W

s-m

21.84

-

-

4.84

-

0.06

17.60 6.13 100.74 t1.54

] 29.76

1.94

-

-

0.17 4.56 5.10 2.32

0.01 5.02 5.76 1.97

3.24

I W

-

d(A) 16 13 12

I m W

W W

m

m

8.8 8.2 7.7 7.4

99.22 1.54

-

I

8.90 d(A) I 18 W 13 W

W

W

9.7 8.8 8.0 7.6

-

-

15.7 7.1 101.8

d(A) 17

5) 42.78 %

-

W

w w

11 10 8.7

w

7.5

s

W

W

w w

S

W S S

s-m m m S S

W

3.3 3.2

4) 41.62 % none 0.06 0.03 1.35 33.89 tr

2.9 tr 3.2 30.6

W

m W

3) 41.1 %

-

-

35.06 none n.d. 1.11 0.02 0.10 7.64 5.50 100.12 1.53

4.6 4.5 4.2

3.2

2) 44.65 % none 1.38 1.80

1) 47.28 % tr 0.36 3.05

SiOz Ti02

S

4.6 4.5 4.3

S

3.8 3.7 3.6 3.5

S

S

s-m S

S

4.6 4.5 4.3

s s s-m

4.6 4.5 4.2

s-m w w

3.8 3.7 3.6

s-m s s-m

3.7

9

3.5

m

s-m

s-m (Continued)

CLAYS AND CLAY MINERALS

75

TABLE 1.19.-Continued d(&

2.6 2.5 2.4 1.73 1.68 1.64 1.54 1.53

I

s s

m-s m m

w s

s

d(A)

2.6 2.5 2.4 2.3 1.74 1.70 1.68 1.56 1.53 1.52

z

d(A)

s-m s s s-m

2.7 2.6 2.5 2.4

s

s s-m

z

d(&

I

d(& 2.9 2.7

2.6 2.5

Z m-s s

s s

m

2.5 2.4 2.13

s s

w

m m m

1.54 152

w s m

m m-w

1.56 1.54 1.53

m-w m m-w

1.56 1.54 1.53

w s

s-m

1) Hirose, Tottori Prefecture. 2) Kiuragi, Saga Prefecture. 3) Yagiyama, Fukuoka Prefecture (Minato and Sudo, 1949). 4) Horokanai, Hokkaido (Minato and Muraoka, 1958). 5 ) Hirose, Tottori Prefecture; nickel-bearing deweylite.

TABLE 1.20. Chemical compositions of “garnierite”, aquacreptite, sepiolite, attapulgite, stevensite, and saponite (Shimoda, 1964) SiOa Ti02 AlzOa Fez03

MgO NiO CUO MnzOa MnO CaO NazO KzO HzO(+) HaO(-) Total

1) 44.78%

2) 49.46%

3) 50.53%

4) 52.97%

5) 53.35%

2.20 0.44 8.93 24.41

1.55 0.49 27.16 tr

0.74 0.93 28.04

0.86 0.70 22.50

15.44 2.12 6.60

0.32 27.47

7) 43.62% 0.00 5.50 0.66 24.32

0.21 0.97 0.03 0.03 7.17 6.69 100.27

0.06 2.85 0.08 0.04 5.48 17.42* 100.03

6) 57.30% 0.08

0.87 3.14 0.64 0.04

0.24 0.02

0.26 0.03

9.79 8.63 99.86

9.95 10.55 99.42

8.55 10.30 99.38

0.14 8.80 9.90 99.74

1) “Garnierite” from New Caledonia (analyst: Shimoda). 2) Aquacreptite from Miyamori (analyst: Shimoda). 3) Aquacreptite from Hirose (analyst: Shimoda). 4) Sepiolite from Utah (Nagy and Bradley, 1955). 5) Attapulgite from the Shetlands (Stephen, 1954). 6) Palygorskite from Springfield (Faust and Murata, 1953). 7) Saponite from Scotland (Mackenzie, 1957). *At 300’C.

12.00 10.32 98.97

OUTLINE

76 Talc

1

“Garnierite” (New Caledonia)

2

4

5

6

Chrvsotile

I

1

2.5 3

1

I

I

I

l

4

6

8

10

12

l

14 P

Fig. 1.30. Infrared absorption spectra of deweylite as compared with those of talc and chrysotile (Kato and Minato, 1960). Sample numbers: see Table 1.19.

1.3.14. Aquacrep tite

Aquacreptite occurs as a fissure-filling or incrustation in serpentine. Shimoda (1964) pointed out the existence of a family resemblance among minerals such as aquacreptite, “garnierite”, stevensite, palygorskite, sepiolite and saponite. In chemical composition (Table 1.20), aquacreptite is closest to “garnierite” with the nickel replaced by magnesium. The aluminum and H20( -) contents are less in aquacreptite than in saponite.

CLAYS AND CLAY MINERALS

77 I

1

1

L

1

-1 0

1

I

800

200 Temp. (“C)

Fig. 1.31. DTA and TG curves for “garnierite,” aquacreptite, stevensite, saponite, attapulgite and sepiolite (Shimoda, 1964). A: Garnierite, from New Caledonia. D: Saponite, after Mackenzie (1957). B: Aquacreptite, from Miyamori. E: Attapulgite, from Kawahage. F : Sepiolite, from Kyoto. C: Stevensite, after Randall (1959).

In its DTA curves, aquacreptite resembles both “garnierite” and stevensite (Fig. 1.31). In its TG curves (Fig. 1.31), it is very close to “garnierite”. Weight loss occurs continuously in the 180-800°C region, so that aquacreptite (like “garnierite”) resembles attapulgite and sepiolite in this respect. In its X-ray powder diffraction patterns, aquacreptite again resembles “garnierite”. A 10-1 1 8, peak tails towards the low angle side and is unaffected by treatment with ethylene glycol. It should be noted on the other hand that the 11 a peak of aquacreptite contracts slightly to 10 8, after heating at about 200°C (Table 1.21). Electron micrographs of aquacreptite and “garnierite” reveal aggregates of flake-shaped units. These, however, have very fine folding and appear to be composed of fine fibers. The energy of dehydration below 200°C is higher in aquacreptite than in montmorillonite, and intermediate between a- and /3-sepiolites (Table 1.22). On the basis of the above data, Shimoda proposed the structural model for aquacreptite shown in Fig. 1.32. This may be regarded as a hybrid of a chainlike structure such as sepiolite or palygorskite, and a layered structure such as

OUTLINE

78 TABLE 1.21. X-ray powder diffraction data for "garnierite" and aquacreptite (Shimoda, 1964) Aquacreptite (Hirose) 700°C

Room temp. d(&

Z

11.7 5.0 4.595 3.67 3.218 2.576 1.732 1.592

20b 4 35 5 12b 18 6 13

1ooo"c d(h 10.39 33 5.063 4.458 4.667 28 4.130 3.195 3.241 14 2.910 2.597 14 2.554 2.513 1.534 11 1.988 1.799 1.638 Aquacreptite (Miyamori) 1OOo"C 700°C

d(&

Room temp.

d(& 10.63

Z

d(h 11.04 5.06 4.620 3.73 3.223 2.560 2.307 1.726 1.534

30b 4 45 4 20 40b 5 10 35

Z

4.615

38

3.229 2.560 2.280 1.697 1.536

20 27b 6 5 23

Z

d(&

42b 27b 5 9 20b 33b 9 36

10.23 4.620

I 50b 36b

3.215 2.550

25b 30b

1.529

25

Z 5 10 30 70 32 22 32 12 5 8

Z

d(&

27b

4.457 3.229 3.151 2.937 2.562 2.149 2.039 1.653 1SO7

"Garnierite" (New Caledonia) 700°C

Room temp.

d(A) 10.16 4.595 3.644 3.373 3.200 2.533 1.726 1.527

Z

10 66

63 28b 10 11 15 9 1OOo"C

d($

Z

d(h

I

5.151 4.329 4.130 3.897 3.735 3.490 3.299 2.882 2.769 2.576 2.513 2.447

13 13 10 15 8 26 4 5 50 14 50 85

2.257 2.159 2.026 1.742 1.668 1.663 1.612 1.489 1.474 1.390 1.345 1.307

21 12 8 48 8 7 10 15 28 10 9 7

CLAYS A N D CLAY MINERALS

79

TABLE 1.22. Energy of dehydration of montmorillonite, sepiolite and aquacreptite (Shimoda, 1964) Montmorillonite 8-Sepiolite Aquacreptite (from Miyamori) a-Sepiolite

E (kcal/mol of HzO) 4.6 5.4 6.5 7.8

b-axis

Fig. 1.32.

Structure model of aquacreptite (Shimoda, 1964).

most phyllosilicates. X-ray intensities calculated from this model agree fairly well with observed values. 1.3.15. Allophane and imogolite

Volcanic ash, pumice beds and glassy tuffs are widely distributed in Japan, and have suffered extensive weathering. Allophane and imogolite are common constituents of the weathering products of these materials. Studies on the allophane in volcanic ash soils were begun in 1913 by Seki, and have been particularly active since around 1954. The work has involved a broad range of topics from clay and soil mineralogy, to agriculture and the chemical industry. Imogolite was discovered and confirmed by Aomine and Yoshinaga (1955) and Yoshinaga and Aomine (1962). Subsequently, it has been found in volcanic ash soils at numerous localities, and the work on it has come to involve many soil scientists in Japan. Imogolite is also known from volcanic ash soils in several

80

OUTLINE

other countries, and has been confirmed to represent one of the principal constituent minerals of volcanic ash soils. Recent progress on imogolite has revealed that this mineral contains a new type of crystal structure. It is thus established as a new clay mineral, and has provided a new approach to the study of the mechanisms of alteration of volcanic glass fragments in soils. Details concerning allophane and imogolite are given in Chapter 4.

1.3.16. Spherulitic halloysite Sudo and his collaborators have reported on the basis of electron micrographs that some kaolin clays are composed of spherules (Sudo, 1951b, 1953; Sudo, Minato and Nagasawa, 1951;Sudo and Ossaka, 1952; Sudo and Takahashi, 1956; Sudo, Kurabayashi et al., 1964). These clays consist largely of halloysite (10 A) and occur in the weathering zone of rhyolitic tuffs and tuffaceous sediments. The spherules are usually composed of a central spherule with fine fibrous particles projecting radiaIly out from it. Similar materials have also been reported by Alietti (1959), Chen (1959), Siefferman and Millot (1969), Tichet (1969), etc. Sudo and Takahashi (1956) studied the morphology of the spherules in detail and pointed out several morphological characters, as follows. (1) The central spherulitic bodies and fibrous particles are usually almost uniform in size and shape in samples collected from one locality. However, they tend to show slight differences from locality to locality. (2) The fibrous particles which are associated with central spherulitic bodies of relatively small size, are usually extremely fine, like “curled hair”. (3) The length and width of the fibrous particles tend to increase with increasing size of the central spherules. When the spherules are sufficiently large, the shape of the fibrous particles often appears as a “horn”. This shape probably results from peeling of a thin surface layer from the central spherule and then partial rolling of the layer into a tubular particle. The horn-shaped particle appears to have rolled more into a tubular form at its apex, while its base tends to be spread out over the surface of a central spherulitic body. The fibrous particles are also found as isolated particles in the interspaces between spherules. The isolated particles usually have a better-defined shape than the “curled hair”type, but still commonly exhibit partially tubular shapes and undulated edges. They are ill-defined in shape compared with usual halloysite (10 A). (4) In samples composed of large spherulitic bodies, isolated fibrous particles tend to have a well-defined tubular form like halloysite (10 A). The relative amount of spherulitic bodies with attached elongate particles tends to fall in comparison with the amount of the isolated particles. (5) The spherulitic bodies in (1)-(4) show concentric textures, and occasionally polyhedral outlines. Sudo and Takahashi named these particles “chestnut shell-like particles”,

CLAYS AND CLAY MINERALS

81

and proposed that the variation in shape outlined in (1)-(4) may derive from advancing crystallization of allophane into halloysite (10 A). Kurabayashi and Tsuchiya studied the geology and mineralogy of the volcanic ash beds in Japan, concentrating on the Kanto volcanic ash beds (socalled Kanto Loam) which are widely distributed in the Kanto Plain (Tsuchiya and Kurabayashi, 1958; Kurabayashi and Tsuchiya, 1959, 1960, 1962; Sudo, Kurabayashi, Tsuchiya and Kaneko, 1964). The Kanto volcanic ash beds may be divided into the following horizons (from upper to lower): Tachikawa, Musashino, Shimosueyoshi, and Tama. The many profiles studied extended from the uppermost layer of the Tachikawa to the lowermost layer of the Tama (the depth of which is less than about 40 m). X-ray powder diffraction patterns, electron micrographs, and DTA curves revealed that the uppermost horizon (Tachikawa) is entirely composed of allophane, and the amount of halloysite (10 A) tends to increase downwards. The following trends were confirmed. (1) Generally speaking, the variation in morphology of the particles with increasing burial depth is from item (1) towards item (4)above. (2) The uppermost horizon is composed entirely of allophane which occurs as aggregates of extremely fine particles of mean size 0.05 p . In some cases, with increasing depth, the aggregates are found to have coagulated into larger particles which are roundish in shape but not completely spherical. At this stage, fibrous particles are absent and the X-ray powder diffraction peaks of halloysite (10 A) are not discernible. (3) Going toward lower horizons, “chestnut shell-like particles” appear and the X-ray powder diffraction peaks of halloysite (10 A) become discernible. (4) At further depth, the following general tendencies are apparent : the X-ray intensities of halloysite (10 A) increase; the sizes of both the fibrous particles and central spherulitic bodies increase; the shapes of the fibrous particles become better-defined, approaching those of usual halloysite (10 A); the amount of isolated fibrous particles increases relatively as the amount of spherulitic bodies decreases; and finally, the pattern displayed by the particle aggregates becomes one composed entirely of tubular particles of usual halloysite (10 A). Based on the above trends, the authors suggested a series of chemical reactions which might result in the transformation, as follows: volcanic glass (rhyolitic) allophane “chestnut shell-like particles”+halloysite (10 A), broadly advancing with increasing burial depth. Subsequent studies on the alteration of pumice beds in other localities by various authors have revealed that the transformation of allophane to halloysite within them is not necessarily a recrystallization which can be expressed simply as a function of time and increasing burial depth. Tt has been suggested that the degree of transformation may also vary with the chemical, lithological, and sedimentary features of the profiles and sequences intercalated with the pumice beds.

- -

82

OUTLLNE

CLAYS AND CLAY MINERALS

83

Figs. 1.33-1.35. Spherulitic halloysite in the white clays derived from weathered pumice beds occurring in the Yawatama Naegi district, Gifu Prefecture. Photographs: S. Aida, JEOL, Tokyo, Japan. Fig. 1.33A and B. (ogposife)Transmission images. Fig. 1.34A-D (above). Scanning images. Fig. 1.35 (see overleaf)

Recent electron microscopes with high resolution power have revealed the inner and outer textures of the particles in more detail than previously (Sudo and Yotsumoto, 1977). Figs. 1.33-1.35 show micrographs of white clays altered from pumice beds in the Yawatama Naegi district, Nakstsugawa City, Gifu Prefecture. The white clays are intercalated with kaolin clay beds and represent weathering products from pumice fragments. The kaolin clay beds occur as detrital sediments derived from weathered granitic basement rocks, and are largely composed of usual kaolinite and tubular halloysite. Fig. 1.33A shows the concentric texture of the spherulitic bodies of the white clays. Occasionally, aggregates of extremely fine particles (as indicated by

84

OUTLINE

a cross), which seem to consist of a colloidal material like allophane, are found in association with the spherulitic bodies. Fig. 1.33B shows an interestingly shaped particle (indicated by a small closed circle) which appears to be a result of peeling and partial rolling of a thin surface layer of the spherulitic body. It should be noted in Figs. 1.33 A and B that the shape of the elongated particles of halloysite with a partially tubular form and undulating edges is not so welldefined as in usual halloysite (10 A) as indicated by the small open circles. Figs. 1.34A-D are scanning micrographs. Fig. 1.34A-B shows uneven surfaces of spherulitic bodies that appear as though they had been piled up as curved tiles. Figs. 1.34C and D illustrate the inner textures of spherulitic bodies; the particles in Fig. 1.34C are apparently hollow in their central part. Fig. 1.35 shows a 7 A-

Fig. 1.35. Electron diffraction pattern.

CLAYS AND CLAY MINERALS

85

lattice image which is certainly due to halloysite (7 A), a dehydration product of halloysite (10 A) under vacuum conditions. Based on the data so far given for the particles under consideration, it is difficult to develop a unique name for them due to their complex variation in shape and mineralogical properties. The name "chestnut shell-like particles" has been used to illustrate the overall morphology. Spherulitic bodies that are dominantly composed of halloysite may be called spherulitic halloysite. The name allophane-halloysite spherules has been used in the sense of stressing their genetic relation to allophane on the one hand and to halloysite on the other, and of emphasizing their occurrence as incorporated bodies of allophane and halloysite, as suggested by the presence of weak X-ray peaks of halloysite. 1.3.17. Hisingerite and penwithite

Hisingerite and penwithite (neotocite) are well known as poorly crystalline clay minerals. Penwithite was first descrbied in Japan by Kato (1924) from the Kawazu mine, Shizuoka Prefecture (Table 1.23). This mine involves gold-silver veins in Miocene propylite with abundant manganese minerals as gangues of penwithite, innesite, etc. Penwithite has also been found in several other manganese deposits such as at the Kaso mine, Tochigi Prefecture, which involves a contact deposit of manganese in Paleozoic quartzite (Table 1.23) (Yoshimura, 1938). Penwithite occurs as brown to black-colored masses having a conchoidal fracture. The first report on hisingerite in Japan was probably that on the chemical analysis of a sample from the Nakakosaka mine (iron deposit), Gunma Prefecture (Milne, 1879). Subsequently, hisingerite has been found as a gangue mineral associated with various metallic ore deposits such as epithermal copper-quartz veins and hydrothermal to pneumatolytic tin veins. Sudo and Nakamura (1952) reported the mineralogical properties of hisingerite from the Kawayama mine, Yamaguchi Prefecture (Table 1.23, Figs. 1.36, 1.37). This mine involves cupriferous pyrrhotite deposits with a bedded form along a thrust zone in graphite-sericite-quartz schist. The ore is composed largely of pyrrhotite associated with chalcopyrite, sphalerite, pyrite, etc. The gangue minerals consist of hedenbergite, actinolite, garnet, calcite and quartz. Hisingerite fills fissures and fault zones in the ore bodies or exists as small patches in the ore. There is no clear relation between the amount of hisingerite and depth from the present surface, hisingerite being found even at considerable depths. The X-ray powder diffraction pattern is composed of only three broad bands, which are close to the (hk)-bands of clay minerals having a layered lattice. On the basis of the chemical composition, these bands are considered to represent crystallites of nontronite. Subsequent studies on hisingerite have also indicated that crystallites of so-called hisingerite consist of nontronite (Bowie, 1955) or iron-saponite (Whelan and Goldich, 1961). Electron micrographs of

I

I

I

I

I

0

-

38 36 34 32 : 40

30

20 18 16 14 12 10 8

3

Wave number (cm-') (X100)

6 4

CLAYS AND CLAY MINERALS

87

the Kawayama hisingerite reveal that it is composed of aggregates of fine flakes with strong folding. Kohyama and Sudo (1975) have described the hisingerite from Oya, Tochigi Prefecture (Table 1.23, Figs. 1.36, 1.37). The material occurs among weathered clayey volcanic rock fragments in Oya-ishi (see section 1.3.4) consisting of ironbearing montmorillonite-beidelliteand iron-saponite. The X-ray powder diffraction pattern is composed of several broad peaks involving a 16 peak, which agrees with those of montmorillonite minerals. The peak system on the DTA curve of the Oya material is close to that of the Kawayama material except for the presence of an extremely weak endothermic peak between 500-600°C. The amount of MgO in the Oya material is less than that in the unweathered rock. Electron micrographs of the Oya material show thin flakes with irregular outlines and curled edges. It appears very probable that the Oya material was derived from iron-montmorillonite and iron-saponite by weathering (p. 42). The intensities of th,: X-ray bands and the endothermic peak between 500600"C, and the content of MgO, are in fact somewhat variable. The data in Table 1.23 and Figs. 1.36, 1.37 are for the sample showing the lowest X-ray and thermal peak intensities, and the lowest content of MgO. Compared with the Kawayama material, the properties of montmorillonite minerals are readily discernible in the Oya material (Table 1.24). Assuming that there is no modification of principal chemical components between hisingerite and its original parent mineral, the chemical formulas should presumably be calculated on the basis of 010(OH)2as shown in Table 1.23, which indicates that both the Qya and Kawayama materials are of the dioctahedral sub-group, and the material reported by Whelan and Goldich is of the trioctahedral sub-group. The parent material of the Oya hisingerite is a mixture of iron-montmorillonite and iron-saponite. It is therefore considered that these materials were transformed into a poorly crystalline material having the chemical composition approaching nontronite, i.e. the Oya hisingerite. The sample reported by Whelan and Goldich has a considerable amount of MgQ and is trioctahedral, so that it is considered to represent a poorly crystalline analog of iron-saponite as these authors stated. Hisingerite may be defined as including very poorly crystalline minerals (analogs) of iron-rich montmorillonite minerals involving the dioctahedral and/or trioctahedral subgroups. There is some question as to whether all hisingerite has been formed from Fig. 1.36. (upper graph, opposite) DTA curves for hisingerite. 1) Kawayama mine, Yamaguchi Prefecture (Sudo and Nakamura, 1952). 2) Qya, Tochigi Prefecture (Kohyama and Sudo, 1975). Fig. 1.37. (lower g r p h s ) Infrared absorption spectra of hisingerite and nontronite (Kohyama and Sudo, 1975). 1-4) Hisingerite. 1) Qya, Tochigi Prefecture (Kohyama and Sudo, 1975). 2) Kawayama mine, Yamaguchi Prefecture (Sudo and Nakamura, 1952). 3) Beaver Bay complex (Whelan and Goldich, 1961). 4) East Besabi (Whelan and Goldich, 1961). 5 ) Nontronite from Spokane, Washington.

88

OUTLINE

TABLE 1.23. Chemical and X-ray data for hisingerite and penwithite Hisingerite

SiOz Ti02 Alz01 Fez03 FeO MnO MgO CaO NazO KzO HzO(+) HzO(-) Total Si A1 Fe3+

1) 27.99 %

2) 40.68 %

34.25 0.54

4.44 28.32 0.20

-

-

7.11 27.89

1.85 1.42 1.50 0.33 6.43 13.70

100.11

98.87

2.33

0.84 2.07 0.05

I

4.00

4) 38.19% 0.01 0.00 19.91 24.64 0.66 2.36 0.61

6.85 6.95

8.40 5.53

4.00

3.64 0.36

}

100.31 400 4.00

2.12

0.01

2.06

.13} 0.28

0.25 0.04

z

d(i)

z

16.1

w

K

I

4.00

I

0.01

0.281

d(i)

0.45

3) 42.35 % 0.13 3.65 23.28 5.54 0.38 8.22 2.06

99.41

X 5 : ]

3.16}

A1 Fe3+ Fez+ Mg Mn Ca Na

-

Penwithite

::2:*

1.90* 2.99 1.05 0.381 0.03

0.06

0.38

OVi4}

0.14

d(A)

z

7.53 4.33 3.50 2.55

w w w w

1.55 1.21

w w

0.42

d(A) 1

4.44

w

4.51

w

4.51

w

2.61

w

w

w

wb wb vwb vwb

2.54

1.50

2.55 2.45 1.71 1.51

1.70 1.53

w w

3.00

Hisingerite. 1) Kawayama mine, Yamaguchi Prefecture (Sudo and Nakamura, 1952). 2) Oya, Tochigi Prefecture (Kohyama and Sudo, 1975). 3) Beaver Bay complex (Whelan and Goldich, 1961). 4) East Mesabi (Whelan and Goldich, 1961). Penwithite. 1) Kawazu mine, Shizuoka Prefecture (Kato, 1924). 2) Kaso mine, Tochigi Prefecture (Yoshimura, 1938).

1) 39.57%

2) 36.50%

1.59 1.29

1.07 1.47

31.81 0.31 1.03

36.85 6.02

24.30

11.87 6.72

99.90

100.50

89

CLAYS A N D CLAY MINERALS TABLE 1.24. Comparison of the Oya and Kawayama hisingerites ________

-~

___

-

~

Oya hisingerite

Kawayama hisingerite -

Broad reflections of nontronite are observed. The weak basal peaks are also observed. Endothermic peak due to dehydroxylation is scarcely obser ved. Diffuse bands of nontronite and a weak OH-vibration at 3550 cm-l are observed. Most of the iron is ferric and when calculated on the basis of I O ( 0 ) and 2(OH), it shows a dioctahedral structure. Thin small flakes with curled edges, preserving a smectite-like shape. Clear hk reflections are observed.

Broad reflections of nontronite are observed, but the basal peaks are not observed. Endothermic peak due to dehydroxylation is absent. Diffuse bands of nontronite and a weak OH-vibration at 3540 cm-1 are observed. Most of the iron is ferric and when calculated on the basis of 1qO) and 2 (OH), it shows a dioctahedral structure. Fine curled fibers.

~

X-ray reflections

DTA curves

IR spectra Chemical composition

Electron micrographs

Electron diffraction -____

~

_

-

-

Clear hk reflections are observed. ~

_

iron-rich montmorillonite minerals, and also as to whether hisingerite is always formed by surface weathering. Mineralogy texts indicate that hisingerite is found as an alteration product of iron-rich non-clay minerals such as irongarnet, pyrite, etc. The Kawayama material occurs in close association with pyrrhotite, and no iron-rich montmorillonite minerals exist which could be considered as a parent material for the Kawayama hisingerite. There is no indication that the Kawayama material is particularly prevalent in the surface zone, and it is known to occur at depth in appreciable proportions by weight. Another process for the origin of the hisingerite can therefore be suggested as follows: hisingerite was formed as a gel by the alteration of iron-rich non-clay minerals under specific chemical conditions probably involving deep-seated weathering and hot spring action, and nontronite-like crystallites were then produced as a result of crystal nucleation in the gel. 1.3.18. In terstra t ified cIay mineraIs The studies on hydrobiotite by Gruner (1934) can be regarded as the pioneer-

ing work on interstratified clay minerals. Subsequently, and particularly recently with the development of appropriate tools for mineral identification, numerous data have been accumulated. Interstratified clay minerals, although considered rare at the time of their discovery, are now regarded as common constituents of clays, and their importance has been recognized not only in mineralogy and crystallography but also those branches of petrology and geology which deal with clay genesis. In the early stage, one of the significant developments was the finding of certain regular types. In 1950, Bradley (1950) demonstrated that rectorite (a species of doubtful validity in old texts) consisted of a regular inter-

90

OUTLINE

stratification of pyrophyllite-like and vermiculite-like layers. In 1954, Lippmann (1954) discovered a new mineral type-a regular interstratification of magnesian regular interstratifications of chlorite and swelling chlorite-and named it corrensite. In 1954, Sudo, Takahashi and Matsui (1954) discovered another new type-an aluminian regular interstratification of chlorite and montmorillonite. Frank-Kamenetsky, Logvinenko and Drits (1965) clarified that alushtite, which was also included among species of doubtful validity, was of this type and named it tosudite. Studies on this new mineral (tosudite) revealed the existence of aluminum (dioctahedral) chlorite in Japan. Both corrensite and tosudite have now been identified at many localities in Japan and overseas. Alietti (1956) found a new type-a regular interstratification of talc and saponite-and Veniale and van der Marel (1968) later named it aliettite. In 1956, Sudo and Hayashi (1956b) discovered a complex new interstratification in Japanese acid clay deposits which is considered to consist of random interstratifications of montmorillonite and kaolin minerals such as halloysite (10 A) and halloysite (7 A). This interstratification is characterized by X-ray diffraction peaks consisting of extremely broad basal peaks and clearly discernible (hk) peaks. Details will be given in Chapter 5. Kurabayashi and Tsuchiya (1962) reported a similar interstratification in the Shimosueyoshi Loam which is divided into non-marine (lacustrine) and marine deposits. These authors indicated the interesting fact that the distribution of this interstratification in the ShimosueyoshiLoam is limited to deposits formed under marine conditions (Fig. 1.38). Some of the Shimosueyoshimaterials are regarded as a random interstratification of halloysite (10 A) and halloysite (7 A) since an exothermic peak at about 700°C is just visible in samples pre-treated with piperidine. Recently, a number of similar materials has been found and studied in other countries such as the U.S.A. (Schultz, Shepard, Blackmon and Starkey, 1971), Poland (Wiewiora, 1971), England (Wilson and Gradwick, 1972) and U.S.S.R. (Sakharov and Drits, 1973). Research on complex interstratifications has thus become active. The material described by Wiewiora (1971) shows sharp X-ray diffraction peaks and was described as an interstratification of kaolinite and montmorillonite. In 1962, Sudo and his collaborators (Sudo, Hayashi and Shimoda, 1962) gave an overview of interstratified clay minerals based on the “intermediate clay mineral concept” and proposed a new theory for the origin of interstratified minerals. This may be termed “the electric polar hypothesis” since it suggests an electric polarity within the unit structure. Although the polarity is still difficult to detect by the direct method, several workers involving the above authors have continued the work, and the concept has been tested for its validity by several workers overseas. Tettenhorst and Johns (1966) reported an explanation for the effects of glycol or glycerol treatment on montmorillonite that favors the concept. Cole (1966), Lippmann and Johns (1969), and Veniale and van der Marel (1968) reported that the structures and crystalchemical properties of regular interstratifications may also favored the concept. Tomita and his collaborators favored the electric polar hypothesis for explaining

CLAYS AND CLAY MINERALS

91

A

I@

I

I

I

I

I

1

4

TI0

me

I

I

I

L

Tvo 10A,

vo

Fig. 1.38. Distribution of a complicatedointerstratification of montmorillonite and kaolin minerals such as halloysite (10 A) and halloysite (7 A) in the Shimosueyoshi Loam (Kurabayashi and Tsuchiya, 1962). A : For the sake of convenience, the X-ray powder patterns of clays collected from the Shimosueyoshi Loam are divided into five types, I-V. I: The pattern of this interstratification; the basal pea&occurs as broad band extending in the range of 7-9 A. 11,111, and IV: The peak of halloysite (10 A) is dis5ernible; its amount increases in the order I1 < I11 < IV. The weak and broad peak at about 8 A may indicated small amounts of this interstratification. V : Typical pattern of halloysite (10 A). B: Distribution and types of samples collected from the Shimosueyoshi Loam in the Kanto Plain. The distribution of type I is limited almost to within the area of Paleo-Tokyo Bay (shaded) developed in the Shimosueyoshi transgression period.

the synthesis of regular or almost regular interstratifications of mica and expandable layers from micas, which was performed by themselves and by Ueda and Sudo (see section 1.1.15). In 1963, Brindley and Sandalaki (1963) proposed a new concept which may be termed the demixing hypothesis: it suggests a redistribution of cations between exchangeable and non-exchangeable sites. The concept is based on the studies of MCring and Glaeser (1954) on the demixing cations in montmorillonite, and is supported by the work of Sawney (1967) showing the development of long spacings from Ca-vermiculite exchanged progressively with K and Cs ions. Further, it is considered that the effects of the polytypes of parent minerals (Johnson, 1964) or of the (OH) dipole orientation, may possibly give rise to the development of long spacing regularity (Norrish, 1973).

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The intermediate clay mineral concept proposed by Sudo, Hayashi and Shimoda states that intermediate clay minerals which depart from the usual clay minerals in terms of various properties, may be divided into two types: the inierstratified type and the deviation type. The latter is defined as a clay mineral in which no interstratified structure is actually discernible, but the departure is still recognized. The question of the validity or otherwise of the deviation type remains unsolved. The origin of interstratified clay minerals and the identification of the deviation type thus represent significant and interesting problems in modern clay mineralogy. The details of the interstratified minerals are given in Chapter 8. 1.3.19. Zeolites

A detailed description and discussion of zeolites is beyond the scope of the present book. However, studies on zeolites have indicated a close relation between them and clay minerals in terms of their modes of occurrence and origin. A brief account of past and present work on zeolite problems in relation to clays is thus included here. Zeolites have long been known to constitute an important mineral family and have largely been described from the mineralogical viewpoint, although certain properties of zeolites such as cation exchange, absorption, etc. are of considerable interest from the industrial viewpoint. Bradley (1928) and Ross (1928) described the zeolites occurring in sedimentary rocks. These studies then led to a broad range of zeolite research embracing not only the mineralogy but also the petrology and geology of zeolites. The work of Coombs, Ellis, Fyfe and Taylor (1959) on zeolite facies was significant in this respect. In Japan, since the occurrence of zeolite was originally suggested in glassy rhyolite tuffs (Ota and Sudo, 1949; Sudo, 1950a; Sudo, Nishiyama, Chin and Hayashi, 1963), numerous comprehensive reports have been published. Among them, particular attention should be given to the work of Iijima and Utada (1966) and Utada (1965, 1968) concerning the zonal distribution of zeolites in Tertiary tuffs and tuffaceous sediments in relation to their depositional environments and diagenesis. Also significant is the work on the mineralogy of the Green Tuff. This resulted in the finding many kinds of zeolites, and also demonstrated their importance along with clay minerals in studies on modes of occurrence and origin (e.g. Yoshimura. 1964; Kimbara, 1973). For example, laumontite was found in close association with magnesian regular or almost regular interstratifications of chlorite and expandable clay mineral layers. 1.3.20. Sudoite problem

Since the early days of mineralogy, chlorite minerals have been known to constitute a great mineral family. The majority of the abundant data in the mineralogy texts is for the trioctahedral sub-groups. Only cookeite, a mineral known since 1862, is intermediate between the dioctahedral and trioctahedral subgroups. Active discussion has recently centered on dioctahedral chlorite, and

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93

a number of reports has been published. This section gives a brief review of the historical development of research on dioctahedral chlorite. On the basis of the recently recommended nomenclature, and in order to avoid confusion, the earlier studies will be introduced here using the term “Al-rich chlorite” rather than dioctahedral chlorite. In Japan, Al-rich chlorite was first found as a component mineral of a new type of interstratification-aluminian regular interstratification of chlorite and montmorillonite. The first sample from the Kurata Roseki (Sudo, Takahashi and Matsui, 1954) gave a d(U60) value of 1.4919 k 0.002 A, and it was confirmed that the iron and magnesium contents of this sample were negligible, although data for the whole chemical composition were not available. A very similar interstratified mineral from the Kamikita mine (Sudo and Kodama, 1956) gave a d(060) value of 1.506 A and had 6.44 % MgO. The chemical composition was taken to indicate a chlorite layer which was dioctahedral in the octahedral sheets in the silicate layer, and trioctahderal in the octahderal sheet in the hydroxide layer. For short, the sub-group may thus be designated the di.-tri.-subgroup, where the first term refers to the nature of the octahedral sheet in the silicate layer. Muller (1961) reported the occurrence of Al-rich chlorite as a monomineralic crystal in Germany. The material has a d(060) value of 1.491 A and the contents of magnesium and iron are negligible. The chlorite may thus be assigned, as in the case of the Kurata material, to the di.-di.-sub-group. Engelhardt, Muller and Kromer (1962) reported another Al-rich chlorite from Germany. The d(060) value ranges from 1.490 to 1.504 A, and the total number of octahedral cations is 4-5 (Olo(OH)8).In this respect, the material appears to lie in the intermediate range between the di.-di.- and di.-tri.-sub-groups. These authors used the expression “alle dioktaedrischen Vielschichtsilikate mit Chloritstructur unter dem Reihennamen “Sudoit” . . . Hayashi and Oinuma (1964) first reported the occurrence of monomineralic crystals of Al-rich chlorite in Japan from the Honko ore body (stockwork type) of the Kamikita mine. The sample was collected from the same clay zone as the alumir,ian regular interstratification of chlorite and montmorillonite. This sample has 8.63 % MgO, and a d(060) value of 1.52 A. Sudo and Sato (1966), on the basis of a comparison between the observed and calculated X-ray intensities, favored the assignment of the chlorite to the di.-tri. (not tri.-di.)-sub-group. Eggleton and Bailey (1967) carried out a crystal structure analysis of Al-rich chlorite and confirmed it to be of the di.-tri.-sub-group, They stated that the name sudoite should be favored for this mineral type. Successive reports on the occurrence of Al-rich chlorite in other localities followed, and Muller (1967) stressed that the most appropriate subdivision of the chlorite group may be as follows: 33

Sudoit-Chlorit-Gruppe dioktaedrisch Sudoit-Reihe, trioktaedrisch Chlorit-Reihe

OUTLINE

94

He also recommended the following nomenclature for regular interstratifications of chlorite and montmorillonite: dioktaedrisch Sudoit-Montmorillonit 1 : 1 . . . Tosudit

trio ktaedrisch Chlorit-Montmorillonit 1:I . . . Corrensit

In 1966, at the International Clay Conference, Jerusalem, Israel, Sudo proposed the following classification scheme to the Nomenclature Committee of the AIPEA: dioctahedral chlorites trioctahedral chlorites

4d n <5 5
osx+y<2 2<x+yS4,

where n, x, and y are as shown in the following general formula:

(Al~-,Mg~,,2),(3,,,))(Si4-,Al,)Olo(OH)8 Chukhrov 1968, pointed out that Ya. V. Samoilov, in 1906, had described a mineral from the Nagol’ny Ridge ore, which he classified with members of the chlorite group richest in aluminum (up to 48.16% A1203). He termed this mineral “alpha-chloritit.” Lazarenko (1940) confirmed the occurrence of minerals of this type in ore deposits of the Donets Basin and proposed the common name donbassite for them. On the basis of their external appearance, some donbassites have been taken as pyrophyllite, and in some mineralogy texts, the donbassites are assigned to the kaolinite group. Recently, Russian workers (e.g. Drits and Lazarenko, 1967) have clarified that donbassite is a dioctahedral chlorite, and have suggested replacement of the name sudoite with donbassite. Viczihn (1971) has reported that in Hungarian mineralogy, Ghbor Vavrinecz (1936), in his study of the chemical classification of the chlorite group on theoretical grounds, predicted the existence of Al-rich chlorite which is essentially identical to the “alpha-chloritit” reported by Samoilov. Vavrinecz proposed the name “nagolnit” based on the locality of the Samoilov material; this is a more common name than “alpha-chloritit”. Viczian expressed the opinion that the name nagolnit may have priority. The Nomenclature Committee of the AIPEA has recommended the following nomenclature: Group name Sub-groups

Chlorite Dioctahedral chlorite Di,trioctahedral chlorite Trioctahedral chlorite

where “a dioctahedral chlorite is dioctahedral in the silicate layer and in the hyroxide layer. The term di,dioctahedral chlorite is unnecessary. Donbassite is such a mineral. A di,trioctahedral chlorite is dioctahedral in the silicate layer

CLAYS AND CLAY MINERALS

95

and trioctahedral in the hydroxide layer. Cookeite and sudoite belong to this sub-group. Cookeite contains sufficient LinOin its chemical composition. A trioctahedral chlorite is trioctahedral in both layers.” These recommendations are concerned with a general scheme, and the names given can be regarded as representing the end-members. The actual chemical compositions of particular chlorite minerals do not necessarily agree with or even lie close to any one of these end-members, but may vary in the range (forming a series) between two end-members, although current data are still inadequate to show whether or not these series are actually continuous. The above recommendations may involve the following forms : Group Chlorite

Sub-group Species (end-member) Dioctahedral chlorites (4 S n < 5 ) Donbassite (n = 4) Di,trioctahedral chlorite Cookeite, sudoite Tri,dioctahedral chlorite (n = 5) Trioctahedral chlorites ( 5 < y2 5 6) Many species (n = 6)

Tri, dioctahedral chlorite is unknown. The chemical formulas of the end-members may be summarized in ideal form as follows: Donbassite Sudoite Cookeite

Ale+(z13)(Si4-zA1z)010(OH)~ (Mg3-,A12-,)(Si4-zAlz)Olo(OH)~ (LiA14)(Si3AI)OIO(OH)~

1.3.21. Tosudite problem

The data to date on aluminian regular (or almost regular) interstratifications of chlorite and montmorillonite are summarized in Table 1.25. The properties of the expandable layers may be assigned to montmorillonite. The amount of MgO and LizO, the d(060) spacing, and the total amount of octahedral cations (on the basis of (O4,(OH)z0) should decide the nature of the octahedral sheets. The Kurata material (Sudo, Takahashi and Matsui, 1954) may be dioctahedral in all octahedral sheets. This has been confirmed in the Takatama material (Shimoda, 1969). The sample first described under the name tosudite by FrankKamenetsky, Logvinenko and Drits (1963) may be also dioctahedral in all octahedral sheets. A comparison of the observed and calculated X-ray intensities favors the idea that the Kamikita material (Sudo and Kodama, 1956) is composed of chlorite of the di.-tri.-sub-group and montmorillonite, although the total number of octahedral cations is somewhat insufficient. (Ideally, it should be 14.00). A similar conclusion holds for the Huy and Tohoo materials, both of which contain LizO. The occurrence of Li-bearing samples strongly suggests that the chlorite layers may exist as a donbassite-cookeite series. Although future studies are required, in the literature published to date the name “tosudite” has been used

96

OUTLINE

TABLE 1.25. Aluminian regular (or almost regular) interstratifications of chlorite and montmorillonite

cations (040(OH)zo) -___ Kurata. Japan (Roseki deposit) 29.8 (Sudo, Takahashi and Matsui, 10.5 1954) Hanaoka, Japan (Kuroko deposit) 29.6 (Sudo and Hayashi, 1955, 1956b). k0.2 Kamikita, Japan (Kuroko deposit) 29.8 (Sudo and Kodama, 1956). 10.5 Superior, U.S.A. (iron ore deposit) 30.16 (Bailey and Tyler, 1960). Privetny, Crimea, U.S.S.R. 28.5 (quartz veins in Jurassic shale) (Franh-Kamenetsky, Logvinenho and Drits, 1765); proposed as tosudite. -

,

South West Africa (alteration product of beryl) (Heckroodt and Roering, 1965). Minden, Germany (iron ore deposit in Porta Sandstein) (Schellmann, 1966). Uskot, Crimea, U.S.S.R. (soil) (Gradusov, 1968). Takatania, Japan (alteration product of rhyolitic tuffs of wall rocks of gold veins (Shimoda, 1969); reported as tosudite. Igashima, Japan (clays associated with a hydrothermal fluorite deposit in limestone (Imai and Watanabe, 1972); reported as tosudite. Niida, Japan (Kuroko area) (Kimbara and Nagata, 1974); reported as tosudite. Izushi, Japan (Toseki) (Kanaoka, 1968); reported as tosudite. Huy, Belgium (clays in veins in brecciated shale) (Brown, Bourguignon and Thorez, 1974). Tohoo, Japan (Roseki deposit) (Nishiyama, Shimoda, Shimosaka and Kanaoka, 1975); reported as Li-t osud ite.

* Mg-saturated.

30.0*

1.4919 *0.0002

(0.020.71)

1.5057 0.0008 1.506

1.35

0.25

6.44

0.18

13.51

1.507 1.477

(1.25)

1.49

2.18

12

0.68

1.18

0.6

30

G 28.9* 1.493

0.08

29.39

1.503

8.20

tr

28.9*

1.506

3.08

2.77

29.48 k0.2

1.492

0.29

30.0 10.5

12.16

13.83

0.51

13.57

1.04

13.54

REFERENCES

97

for aluminian regular interstratifications composed of chlorite layers which involve donbassite (the di.-di.-sub-group), sudoite (the di,-tri.-sub-group) and probably cookeite (the di.-tri.-sub-group), or series between them. 1.3.22. Corrensite

Corrensite is the mineral name applied by Lippmann (1954) to the magnesian regular interstratification of chlorite and swelling chlorite first reported by Stephen and MacEwan (1956). Similar interstratifications have been described in many subsequent reports, some of which used the term corrensite. However, as pointed out by MacEwan and Ruiz Amil (1959), the published data do not necessarily all agree with that for the original corrensite. These authors suggested the existence of a series of minerals intermediate between the original corrensite and a regular interstratification of chlorite-montmorillonite. It is now accepted that, in the general sense, the properties of the expandable mineral layers of interstratifications tend to be diverse, and this is so in the case of corrensite samples. It is feasible to use the name only for the original corrensite; however, this and allied minerals are normally differentiated by various behavioral tests, and the differences among the mineral samples tend to be continuous in some cases. The other possibility is of course to use the name as a general name for magnesian regular interstratifications of trioctahedral chlorite and expandable minerals.

1.3.23. Aliettite Aliettite is the mineral name applied by Veniale and van der Mare1 (1969) to the regular interstratification of talc and saponite first reported by Alietti (1956). REFEFENCES Aida, T. (1968) Contr. Dept. Geol. Miner., Niigata Univ., 2, 1. Alietti, A. (1956) Rend. Acad. Nuzl. Lincei, Ser. 8,21(3/4), 201. Alietti, A. (1959) Mem. Acad. Nuzl. di Scienze, Lettere e Arti di Modenu, Ser. 6 , I, 24. Allaway, W. H. (1949) Proc. Soil. Sci. SOC.Amer., 13, 183. Altemiiller, H. J. (1962) Z..fu/ Plunz. Dung u. Bodenkunde 99 (2/3), 164. Andrew, R. W., Jackson, M. L. and Wada, K. (1960) Soil Sci. Soc. Amer. Proc. 24,422. Aoki, S . , Kohyama, N. and Sudo, T. (1974) Deep-sea Res. 21, 865. Aoki, S., Oinuma, K. and Kobyashi, K. (1975) Contributions to Clay Minerulozy, Dedicated to Toshio Sudo on the Occasion of His Retirement, 161. Aomine, S. and Yoshinaga, N. (1955) Soil Sci. 79, 349. Aoyagi, K. (1965) J. Jupan. Assoc. Petrol. Tech. 30, No. 4, 1. Aoyagi, K. (1967) Cluy Sci. 3, 37. Aoyagi, K. (1968) Cluy Sci. 3, 54,70. Aoyagi, K. (1969) Clay Sci. 3, 126. Ariizumi, A. (1967) J . Clay Sci. Soc. Jupun. 6 , 74. Bailey, W. S. and Brown, B. E. (1962) Amer. Miner., 47, 819. Bailey, W. S. and Tyler, S. A. (1960) Econ. Geol. 55, 150. Biscaye, P. E. (1964) Amer. Mine?. 49, 1281. Biscaye, P.E. (1965) Bull. Geol. Soc. Amer., 76, 803. Bischoff, J. L. (1972) Cluys Cfay Miner. 20, 217. Bowie, S. H. U. (1955) Bull. Geol. Surv. G . B. 10, 45. Bradley, W. F. (1950) Amer. Miner. 35. 590.

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Bradley, W. H. (1928) Science, 67, 73. Brindley, G. W. and Robinson, K. (1948) Miner. Mag. 28, 393. Brindley, G. W. and MBring, J. (1951) Acta Cryst. 4, 441. Brindley, G. W. and Mering, J. (1953) C. R. XZX Congr. Giol. Int. Alger 1952 18, 201. Brindley, G. W. and Nakahira, M. (1958a) Miner. Mag. 31, 781. Brindley, G. W. and Nakahira, M. (1958b) Nature 181, 1333. Brindley, G. W. and Nakahira, M. (1959) J. Amer. Ceram. SOC.42, 314, 319. Brindley, G. W. and Sandalaki, 2. (1963) Amer. Miner. 48, 138. Brindley, G. W. and Wardle, R. (1970) Amer. Miner. 55, 1259. Brindley, G. W. and Hang, Pham Thi (1973) Clays Clay Miner. 21, 27. Brown, G., Bourguignon, P. and Thorez, J. (1974) Clays Clay Miner. 10, 135. Burst, J. F. (1958) Amer. Miner. 43, 481. Chen, Pei-yuan (1959) Proc. Geol. SOC.China No. 2, 93. Chukhrov, F. V. (1968) Clays Clay Miner. 16, 3. Cole, W. F. (1966) C/ay Miner. 6, 261. Coombs, D. S., Ellis, A. J., Fyfe, W. S. and Taylor, A. M. (1959) Geochern. Cosmochirn. Acta 17, 53. Derr, W. A., Howie, R. A. and Zussman, J. (1962) Rock Forming Minerals, Vol. 3, 38, Longmans. Drits, V. A. and Lazarenko, E. K. (1967) Miner. Sbornik L’vov, Univ., 21, 40. Eggleston, R. A. and Bailey, S. W. (1967) Amer. Miner. 52, 673. Engelhardt, W. von (1942) Z. Krist. 104, 142. Engelhardt, W. von, Miiller, G. and Kromer, H. (1962) Naturwissenschaften 49, 205. Ewell, R. H. and Insley, H. (1935) J. Res. Natl. Bur. Standards 15, 173. Faust, G. T. and Murata, K. J. (1953) Amer. Miner. 38, 973. Fieldes, M. (1957) New Zealand J. Sci. Tech. B 38, 533. Frank-Kamenetsky, V. A., Logvinenko, N. V. and Drits, V. A. (1965) Proc. Intern. Clay Conf. Stockholm 1963, 2, 181. Fripiat, J. J., Jelli, A. N., Poncelet, G. and Andre, J. (1965) J. Phys. Chem. 69, 2185. Gorbunova, N. Z. (1966) Oceanography 6, 215. Gradusov, B. P. (1968) Trans. 9th Intern. Congr. Soil Sci. Adelaide 1968, 111, 21. Griffin, J. J., Windom, H. and Goldberg, E. D. (1968) Deep-sea Res. 15,433. Grim, R. E., Bray, R. H. and Bradley, W. F. (1937) Amer. Miner. 22, 813. Grim, R. E. (1968) Cloy Mineralogy, McGraw-Hill. Gruner, J. W. (1934) Amer. Miner. 19, 557. Gruner, J. W. (1935) Amer. Miner. 20, 699. Hallimond, A. F. (1922) Miner. Mag. 19, 330. Hang, Pham Thi and Brindley, G. W. (1973) Chys Clay Miner. 21, 51. Harada, K., Kodama, H. and Sudo, T. (1965) Canad. Miner. 8, 255. Hasegawa, H., Kondo, M., and Nakagawa, T. (1958) Japanese Patent, No. 244306. Hathaway, J. C. and Carroll, D. (1954) Clays and Clay Miner., Proc. 2nd Nat. Conf., 264. Hauser, E. A. (1950) U. S. Patent, No. 2,531,427, November, 28, 1950. Hayashi, H. (1961) J. Miner. Soc. Japan 5, 101. Hayashi, H., Inaba, A. and Sudo, T. (1961) Cluy Sci. 1, 12. Hayashi, H. and Oinurna, K. (1964) Clay Sci. 2, 22. Hayashi, H. and Oinuma, K. (1965) Amer. Miner. 50, 476. Hayashi, H. and Oinuma, K. (1967) Amer. Miner. 52, 1205. Hayashi, H. (1973) Ind. Health 11, 225. Heckroodt, R. C. and Roering, G. (1965) C/ay Miner. 6, 83. Heddle, F. and Fermore, L. L. (1926) Rec. Geol. Surv. India 58, 141, 330. Helgeson, H. C. (1969) Amer. J. Sci. 267, 729. Hendricks, S. B. (1940) Phys. Rev. 57, 448. Hendricks, S. B. and Teller, E. (1942) J. Chem. Phys. 10, 147. Hendricks, S. B. and Ross, C. S. (1951) Amer. Miner. 26, 683. Henmi, K. and Yamamoto, T. (1965) Clay Sci. 2, 92. Hoe Soeng Gi and Hayashi, M. (1975) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 70, 440. Honda, K. (1915) Sci. Re p. Tohoku Imp. Univ. Ser. 1, 4, 97. Honjo, G., Kitamura, N. and Mihama, K. (1954) Acfa Cryst. 7,511. lijinia, A. and Utada, M. (1966) Sedimenfology 17, 327.

REFERENCES

99

Iiyama, J. T. and Roy, R. (1963) Clays and Clay Miner. Proc. 10th Natl. Conf., 4. Irnai, N. Otsuka, R., Nakamura, T. and Inoue, H. (1966) J. Clay Sci. SOC.Japan 6, 30. Irnai, N., Otsuka, R. and Nakamura, T. (1967) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 57, 39. Imai, N. and Watanabe, K. (1972) Mining Geol. 22, 43. Jshikawa, H. and Tanaka, H. (1959) Chem. and Chem. Znd. 12,514. Iwai, S., Takeshi, H. and Ossaka, J. (1949) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 33, 163. Iwai, S., Tagai, H. and Shimamune, T. (1971) Acta Cryst. 27, 248. Iwao, S . , Kishirnoto, F. and Takahashi, K. (1954) Rept. Geol. Surv. Japan 162. Iwao, S. (1956) Jupan. J. Geol. Geograph. 27, 105. Iwao, S. (1963) Japan. J. Geol. Geogruph. 34, 81. Jagodzinski, H. and Kunze, G. (1954) Neues Jb. Miner. Mh. 137. Johns, W. D., Grim, R. E. and Bradley, W . F. (1954) J. Sed. Petrol. 24, 242. Johns, W. D. and Shimoyama, A. (1972) Amer. Assoc. Petrol. Geol. Bulf. 56, 2160. Johnson, L. J. (1964) Amer. Miner. 41, 556. Kajiwara, Y . (1973) Geochem. J . 7, 23. Kakinoki, J. and Komura, Y . (1965) Acta Cryst. 19, 137. Kanaoka, S. (1968) J. Ceram. Assoc. Japan 76, 72. Kanno, I. (1954) Bull. Kyushu Agr. Expt. Sta. 2, No. 3, 235. Kato, T. (1924) J. Geol. SOC.Tokyo 31, 19. Kato, To. and Minato, H. (1960) J. Miner. SOC.Japan, 5, 11. Kato, To. (1961) Miner. J . 3, 107. Kato, Y. (1965) Soil Sci. Plant Nutr. (Tokyo) 11, 30, 114. Kawamura, K. and Funabiki, S. (1936) 1. Sci, Soil Manure Japan 10, 215. Keller, W. D. and Pickett, E. E. (1949) Amer. Miner. 34, 855. Keyser, W. L. de (1953) Nature 172, 364. Kimbara, K. (1973) J. Japan. Assoc. Miner. Petrol. Econ. Geol68, 311. Kimbara, K. and Shirnoda, S. (1973) Clay Sci., 4, 143. Kimbara, K. and Nagata, H. (1974) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 69, 239. Kimizuka, Y . (1939) J. Ceram. Assoc. Japan. 47, 557. Kitagawa, Y. (1972) Amer. Miner. 57, 751. Kobayashi, K. (1912) J. Ind. Eng. Chem. No. 12. Kobayashi, K. (1919) Sansei-Hakudo (Acid Clay), 1st ed., Maruzen. Kobayashi, K. (1929) Proc. World Eng. Congr. Tokyo 1929, Vol. XXXI. Kobayasi, M. (1940) Sci. Rept. Tohoku Imp. Univ. Ser. 1, 29, 391. Kodama, H. (1957) Miner. J. 2, 151. Kodama, H. (1958) Miner. J. 2, 236. Kodama, H. (1962) Clay Sci. 1, 89. Kodama, H. and Oinuma, K. (1963) Clays Clay Miner. Proc. 11th Natl. Conf., 236. Kohyama, N., Shimoda, S. and Sudo, T. (1971) Miner. J . 6, 299. Kohyama, N., Shimoda, S . and Sudo, T. (1973) Cfays Cfay Miner. 21, 229. Kohyama, N. and Sudo, T. (1975) Clays Clay Miner. 23, 215. Koizumi, M. and Roy, R. (1959) Arne?. Miner. 44, 788. Kozu, S. and Masuda, M. (1926) Sci. Repf. Tohoku Imp. Uiziv. Ser. 3,3, No. 1 , 33. Kubiena, W . L. (1938) Micropedology, Collegiate Press, Iowa. Kurabayashi, S. and Tsuchiya, T . (1959) J. Geol. Soc. Japan, 65, 768. Kurabayashi, S. and Tsuchiya, T. (1960) J. Geol. SOC.Japan, 66, 78. Kurabayashi, S. and Tsuchiya, T. (1962) Chikyu-Kagaku (Japanese), No. 60-61, 16. Kuwabara, T. (1970) J. Clay Sci. SOC.Japan. 9, No. 3-4, 12. Kuwata, T . (1957) Chem. and Chem. Ind. 10, 352. Lacroix, A. (1916) Bull. Soc. Fran~.Mindr. 39, 90. Lazarenko, E. K. (1940) C. R. (Dokbrdy) Acad. Sci. U.S.S.R. 28, 519. Lemberg, Z. (1877) 2. Deut. Geol. Gesell. 29, 495. Lippmann, F. ( 1 954) Heidelberger Beitr. Miner. Petrog. 4, 130. Lippmann, F. and Johns, W. D. (1969) N e i m Jb. Miner. Pefrol. Monatsh. 5,212. Lovering, T . S. (1949) Econ. Geol. Monogr. 1. MacEwan, D. M. C. (1956) Kolloidzschrift. 149, 96. MacEwan, D. M. C. (1958) Kolloidzschrzyf.156,61.

100

OUTLINE

MacEwan, D. M. C. and Ruiz Amil, A. (1959) Kolloidzschrif. 162, 93. Mackenzie, R. C. and Milne A. A. (1953) Clay Miner. Bull. 2, 57. Mackenzie, R. C. (1954) J. Soil Sci. 5, 167. Mackenzie, R. C. (1957) Miner. Mag. 31, 672. Mackenzie, R. C. (1963) Clays Clay Miner. Proc. 11th Natl. Conf., 11. Mackenzie, R. C. (1970) Differential Thermal Analysis, 1, Chap. 18, 498 Academic Press. Maegdefrau, E. and Hofmann, U. (1938) 2. Krist. 98, 31. Marshall, C. E. (1930) Proc. Royal Soc. A 126, 427. Marshall, C. E. (1935) Z. Krist. 90, 8. Matsui, T. (1966) Res. Znst. Nat. Res. 67. Matsumoto, K. (1968) Earth Sci. Rept. Hiroshima Univ. No. 16, 1. Mering, J. and Glaeser, R. (1954) Bull. Soc. Franc Miner. Cristallog., 77, 519. Midgley, H. G. and Gross, K. A. (1956) Clay Miner. Bull. 3, 79. Milne, J. (1879) Miner Mag. 3,97. Minato, H. and Muraoka, H. (1958) J. Miner. SOC.Japan 3, 626. Minato, H. (1966) J. Clay Sci. SOC.Japan, 6, 22. Minato, H., Imai, N. and Otsuka, R. (1969) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 61, 125. Miyamoto, N. (1957) Miner. J. 2, 193. Mossbauer, R. L. (1958) Z. Phys. 151, 124. Mori, T. and Sasaki, S. (1956) Bull. Hokkaido, Nat. Agric. Expt. Sfa., No. 71, 13. Morimoto, R., Nakamura, K., Tsuneshi, Y., Ossaka, J. and Tsunoda, N. (1967) Bull. Earthquake Res. Znst. 45, 241. Muller, G. (1961) Neues Jb. Miner. Monatsh. 112. Miiller, G. (1967) Contr. Miner. Petrol. 14, 176. Mukaiyama, H. (1954) J. Fac. Sci. Univ. Tokyo Sec. TI, 9, Part 11. Muraoka, H., Minato, H., Takano, Y. and Okamoto Y. (1958) J. Miner. SOC.Japan 3, 381. Nagasawa, K. (1961) J. Earth Sci., Nagoya Univ., 9, 129. Nagasawa, K., Brown, G. and Newman, A.C.D. (1974) Clays CZay Miner. 22,241. Nagata, H. Shimoda, S. and Sudo, T. (1974) Clays Clay Miner. 22, 285. Nagy, B. and Bradley, W. F. (1955) Amer. Miner. 40, 885. Nakahira, M. (1952) J. Sci. Res. Znst. Tokyo 46, 268. Nakajima, Y., Watanabe, Ta. and Sudo, T. (1972) J. Appl. Cryst. 5, 275. Nakamura, T. (1961) J . Inst. Polytech. Osaka City Univ. Ser. G. 5, 53. Neuwham, R. E. and Brindley, G. W. (1956) Acta Cryst. 9, 759. Nishiyama, T. and Shimoda, S. (1974) J. Toyo Univ. Gen. Educ. (Nat. Sci.) No. 17, 1. Nishiyama, T., Shimoda, S., Shimosaka, K. and Kanaoka, S. (1975) Clays Clay Miner. 23, 337. Noll, W. (1935) Neues Jb. Miner. Geol. Beilage Bd. A 70, 65. Norrish, K. (1973) Proc. Intern Clay Conf. 1972 Madrid, 417. Oinuma, K. (1964) J. Toyo Univ. Gen. Educ. (Nut. Sci.) No. 5, 23. Oinuma, K. and Hayashi, H. (1965) Amer. Miner. 50, 1213. Oinuma, K. and Kobayashi, Ka. (1966) CZap Clay Miner. Proc. 14th Natl. Conf., 209. Okino, B. (1967) J. Clay Sci. SOC.Japan 6, 81. Okuda, S. and Williamson, W. 0. (1964) Clays Clay Miner. Proc. 12th Natl. Conf., 223 Ossaka, J. (1975) Gendai-Kagakic (Japanese) October issue, 12. Ota, S. and Sudo, T. (1949) J. Geol. Soc. Japan 55, 242. Otsubo, Y.and Kato, T. (1954) J. Chem. Soc. Japan 75, 456. Paulik, F., Paulik, J. and Erdey, L. (1958) Z. Anal. Chem. 160, 241. Pedro, G . (1967) Bull. Group Frangais des Avgiles X I X , 69. Porrenga, D. H. (1968) Clay Miner. 7, 421. Quakernoat, J. (1970) Clay Miner. 8, 491. Radoslovich, E. W. and Norrish, K. (1962) Amer. Miner. 47, 599. Radoslovich, E. W. (1962) Amer. Miner. 47, 617. Randall, B.A.O. (1959) Miner. Mag. 32, 218. Ross, C. S. (1928) Amer. Miner. 13, 195. Ross, C. S. and Kerr, F. F. (1934) U.S. Geol. Surv. Prof. Pap., 155-G, 135. Saito, H., Otsuka, R., Iwata, S. and Tsuchimoto, K. (1964) Waseda Univ. Bull. Sci. Eng. Res. Lab. No. 27,26.

REFERENCES

101

Saito, H. (1969) Thermal Analysis (ed. R . F. Schwenker and P. D. Garn), 1, 11, Academic Press. Sakharov, B. A. and Drits, V. A. (1973) Clays Clay Miner. 21, 15. Sasamoto, Z. (1895) J. Geograph. Tokyo 7, 228. Sato, M. (1969) 2. Krist. 129, 388. Sato, M. and Kizaki, Y. (1972) Z. Krist. 135, 219. Satoh, S. (1923) Sci. Rept. Tohoku Imp. Univ. Ser. 3, 1, 157. Sawney, B. L. (1967) Clays Clay Miner. 15, 75. Schellmann, W. (1967) Proc. Intern. Clay Conf. Jerusalem 1966,2, 53. Schneider, H. (1927) J. Geol. 35, 296. Schultz, L. G., Shepard, A. O., Blackmon, P. D., and Starkey, H. C. (1971) Clays C h y Miner. 19, 137. Schltz, L. G. (1960) Clays and Clay Miner., Proc. 7th Nat. Clay Conf., 216. Seki, T. (1913) Die Landwirtschajtlichen Versuchs-Stationen79/80, 871. Seki, T. (1928) Third Pan-Pacific Congr. Sci. Congr. Tokyo, 11, 1936. Shimoda, S. (1964) Clay Sci. 2, 8. Shimoda, S. (1965) Clay Sci. 2, 138. Shimoda, S. (1967) Sci. Rept. Tokyo Kyoiku Daigaku Sec. C, 9, No. 92, 263. Shimoda, S., Sudo, T., and Oinuma, K. (1969) Proc. Intern. Clay Conf., 1969, Tokyo, 1, 197. Shimoda, S. (1969) Clays Clay Miner. 17, 179. Shimoda, S . (1970) Clays Clay Miner. 18, 269. Shimosaka, K., Kawano, M., and Sudo, T. (1976) Clay Sci. 5, 31. Shimoyama, A. and Johns, W. D. (1971) Nature 232, 140. Shioiri, M. (1934) Nihon Gakujursu Kyokai Hokoku (Japanese) 10, 694. Shioiri, M. (1935) Trans. 3rd Intern. Congr. Soil Sci., 3, 70. Shioiri, M. and Fukuzawa, T. (1951) J. Sci. Soil Manure Japan 22, 13. Shirozu, H. (1958) Miner. J. 2,209. Shirozu, H. and Bailey, S. W. (1965) Amer. Miner. 50, 868. Shirozu, H. and Bailey, S. W. (1966) Amer. Miner. 51, 1124. Shirozu, H. and Higashi, S. (1972) C/ay Sci. 4, 137. Siefferman, G. and Millot, G. (1969) P,oc. Intern. Clay Conf. Tokyo 1969, 1, 417. Stephen, I. and MacEwan, D.M.C. (1951) C k y Miner. Bull. 1, 157. Stephen, 1. (1954) Miner. Mag. 30, 471. Sudo, T. and Anzai, T. (1942) Proc. Imp. Acad. Tokyo 18,400. Sudo, T. (1943) Bull. Chem. Soc. Japan 18, 281. Sudo, T. (1945) Bull. Chem. Soc. Japan 22, 25. Sudo, T. and Minato. H. (1949) Japan. J. Geol. Geograph. 21, 11. Sudo, T. (1950a) J. Geol. SOC.Japan 56, 13. Sudo, T. (1950b) Proc. Japan Acad. 26, 91. Sudo, T. (195lb)Science 113, 266. Sudo, T. (1951a) J. Geol. Soc. Japan 57, 347. Sudo, T., Nagasawa, K., Amafuji, M., Kimura, M., Honda, S., Muto, T. and Tanemura, M. (1952) J, Geol. Soc. Japan 58, 115. Sudo, T., Minato, H. and Nagasawa, K. (1951) J. Geol. Soc. Japan 57,473. Sudo, T. and Ossaka, J. (1952) Japan. J. Geol. Geograph. 22, 215. Sudo, T. and Nakamura, T. (1952) Amer. Miner. 37, 618. Sudo, T. and Ota, S. (1952) J. Geol. Soc. Japan 58, 487. Sudo, T. (1953) Miner. J. 1, 66. Sudo, T., Takahashi, H. and Matsui, H. (1954) Nature 173, 261 ; Japan. J. Geol. Geograph. 24, 71. Sudo, T. (1954) Clay Miner. Bull. 2, 96. Sudo, T. (1954a) J. Geal. Soc. Japan 59, 18. Sudo, T. (1954b) Clay Miner. Bull. 2, 96. Sudo, T. and Hayashi, H. (1955) Sci. Rept. Tokyo Kyoiku Daigaku Sec. C , 3, No. 25, 281. Sudo, T. and Takahashi, H. (1956) Clays Clay Miner. Proc. 4th Natl. Conf., 67. Sudo, T. and Kodama, H. (1956) Z. Krist. 109,4. Sudo, T. and Hayashi, H. (1956a) CZays Clay Miner. Proc. 4th Nat. Conf., 389. Sudo, T. and Hayashi, H. (1956b) Nature 178, 1115. Sudo, T. and Hayashi, H. (1957) Miner. J. 2, 187.

102

OUTLINE

Sudo, T., Hayashi, H. and Yokokura, H. (1958) Clay Miner. Bull. 3, 258. Sudo, T. Oinuma, K. and Kobayashi, Ka. (1961) Acta Universitatis Carolinae-Geol. Suppl. 1, 189. Sudo, T., Hayashi, H. and Shimoda, S. (1962) Clays Clay Miner. Proc. 9th Natl. Conf., 378. Sudo, T., Nishiyama, T., Chin, K. and Hayashi, H. (1963) J. Geol. SOC.Japan 69, 1. Sudo, T., Kurabayashi, S., Tsuchiya, T. and Kaneko, S. (1964) Trans. 8th Intern. Congr. Soil Sci. Bucharest-Rumania 1964, Vol. 111, 1095. Sudo, T. and Sato, M. (1966) Proc. Intern. Clay Conf. 1966 Jerusalem, 1, 33. Sudo, T. and Yotsumoto, H. (1977) Clays and Clay Miner., 25, 155. Suito, E., Arakawa and Yoshida, T. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 757. Sumi, K. (1968) Geol. Surv. Japan Kept. 225. Takahashi, J. and Yagi, T. (1929) Econ. Geol. 1, No. 2, 64. Takahashi, H. (1959) Bull. Chem. Soc. Japan 32, 235, 245, 252, 381. Takeda, H. and Donney, J.D.H. (1966) Acta Cryst. 20, 638. Takeshi, H. and Shiraki, Y. (1969) “The Clays ofJapan” ( S . Iwao, Ed.), Geological Survey of Japan, 89. Takeuchi, Y. (1965) Clays Clay Miner. Proc. 13th Nat. Conf., 1. Tamamushi, B. (1937) Kolloid-2.79, 300. Tamura, T. (1958). J. Soil Sci. 9, 141. Tazaki, Ka. and Tazaki, KO.(1975) Contributionsto Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 145. Tettenhorst, R. and Johns, W. D. (1966) Clays Clay Miner. Proc. 13th Natl. Conf., 85. Tokunaga, M. (1955) Mining Geol. 5 , 1. Tomisaka, T. and Kato To. (1963) J. Miner. SOC. Japan. 6, 209. Tomita, K. and Sudo, T. (1968) Nature 217, 1043. Tomita, K. and Sudo, T. (1971) Clays Clay Miner. 19, 263. Tomita, K. and Dozono, M. (1972) Clays Clay Miner. 20, 225, Trichet, J. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 443. Tsuchiya, T. and Kurabayashi, S. (1958) J. Geol. Soc. Japan 64, 605. Tsuzuki, Y. and Nagasawa, K. (1969) Clay Sci. 3, 87. Tsuzuki, Y. and Mizutani, S. (1971) Contr. Miner. Petrol. 30, 15. Tsuzuki, Y., Mizutani, S., Shimizu, H. and Hayashi, Hir. (1974) Geochem. J. 8, 1. Twenhofel, W. H. (1939 Principles of Sedimentation, 401, McGraw-Hill Book. Ueda, N., Hang, Pham Thi and Brindley, G. W. (1973) Clays Clay Miner. 21,41. Ueda, S . and Sudo, T. (1966) Nature 211, 1393. Utada, M. (1965) Sci. Pap. Coll. Cen. Educ. Univ. Tokyo 15, 173. Utada, M. (1968) Sci. Pap. Coll. Gen. Educ. Univ. Tokyo 18, 279. Veniale, F. and van der Marel, H. W. (1968) Contr. Miner. Petrol. 17,237. Veniale, F. and van der Marel, H. W. (1969) Proc. Intern. Clay Conf., 1969, Tokyo, 1,233. Vicziin, I. (1971) Folditani Kozlony, Bull. Hungarian Geol. SOC.101, 69. Wada, K. (1958) Soil and Plant Food. (Tokyo) 4, 137. Wada, K. (1959) Soil. Sci. 87, 352. Wada, K. (1961) Amer. Miner. 46, 78. Wada, K. (1963) Amer. Miner. 48, 1286. Wada, K. (1965) Amer. Miner. 50, 924. Walker, G. F. (1949) Nature 164, 577. Warren, B. E. and Averbach, B. L. (1950) J. Appl. Phys. 21, 595. Watanabe, Ta. (1968) Amer Miner. 53, 1015. Watanabe, Y. (1966) BuIJ. Natl. Inst. Agr. Sci. Japan Ser. B, No. 16, 91. Weiss, A. (1956) Z. Angew Allgem. Chem. 284, 247. Weiss, A. (1961) Angew. Chem. 73, 736. Weiss, A., Thielepape, W., Goring, G., Ritter, W. and Schafer, H. (1963) Proc. Intern. Clay Conf. 1963, 1, Stockholm, 287. Whelan, J. A. and Goldich, S. S. (1961) Amer. Miner. 46, 1412. Wiewiora, A. (1971) Clays Clay Miner. 19, 415. Wilson, M. J. and Gradwick, P. D. (1972) CJay Miner. 9, 435. Wise, W. S. and Eugster, H. P. (1964) Amer. Miner. 47, 1031.

REFERENCES

103

Yada, K. (1963) Acta. Cryst. 23, 704. Yagi, T . (1929) J . Japan. Assoc. Miner. Petrol. Econ. Geol. 3, No. 1, 15. Yagi, T (1930) J . Japan. Assoc. Miner. Petrol. Econ. Geol. 3, No. 2,9. Yagi, T . (1932a) J . Jopan. Assoc. A4iner. Petrol. Econ. Geol. 7, No. 3 , 107. Yagi, T . (1932b) J . Japan. Assoc. Miner. Petrol. Econ. Geol. 7, No. 3, 220. Yamada, H., Iwai, S. and Ossaka, J. (1969) Proc. Intern. Clay Conf. Tokyo, 1969, 1, 359. Yoshiki, B. (1944) J . Japan. Assoc. Miner. Petrol Econ. Geol. 12, 107, 165, Yoshiki, B. (1958) “Mineral Technology”, Gihodo, Tokyo, Japan. Yoshimura, To. (1938) J. Geol. SOC.Japan 45, 187. Yoshimura, Ta. (1964) J . Miner. SOC.Japan 7 , 45. Yoshinaga, N. and Aomine, S . (1962) Soil Sci. Plant Nutr. (Tokyo) 8, 6. Zussman, J., Brindley, G. W. and Comer, J. J. (1957) Amer. Miner. 43, 133. Zvyagin, B. B. (1967) Electron Diffraction Analysis of Clay Mineral Structure (Transl. S . Lyse), Plenum Press.

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Chapter 2 Weathering of volcanic ash and other pyroclastic materials Keinosuke NAGASAWA

The Japanese Islands are extensively covered by pyroclastic materials, such as volcanic ash, pumice and scoria, ejected from the many Quaternary volcanoes. These pyroclastic materials have been subject to weathering under surface conditions or have been altered at depth after burial to form various kinds of clay minerals. The processes of clay mineral formation have formed the subject of study of many clay mineralogists in Japan. 2.1.

MINERALOGY OF VOLCANIC ASH SOILS

Many Quaternary volcanoes occur in Japan, especially in central and northeastern Honshu, Hokkaido, and Kyushu (Fig. 2.1). Volcanic ashes, mostly basaltic, andesitic or dacitic in composition, originating from these volcanoes were deposited not only on the volcanoes themselves but also on hills, terraces, or sometimes alluvial plains to the east of them. Since these ashes are fine-grained and permeable, they are liable to be weathered into soils under the humid and temperate climate prevalent in Japan. The volcanic ash soils so formed consist mainly of amorphous materials and are characterized by a thick, loose, darkcolored A horizon rich in humus. The name “Ando soils” has been given to this soil type after the Japanese word “ando” which literally means dark soil. The area of Japan covered by volcanic ash soils has been estimated at about 50,000 km2, i.e. about 14% of the total land area (Ministry of Agriculture and Forestry, 1964). The distribution of these soils is indicated in Fig. 2.1. Pumice or scoria fall deposits are often intercalated with the volcanic ash deposits. Such pumice or scoria has also been weathered into amorphous material similar to that composing volcanic ash soils, although the rate of weathering appears to be lower. 2.1 .I. Allophane

Kawamura and Funabiki (1936) were the first to show by X-ray diffraction studies that Japanese volcanic ash soils are rich in amorphous material. This amorphous material was subsequently established as allophane by the mineralogical examinations of Sudo (1953a, 1954), Aomine and Yoshinaga (1955), 105

WEATHERING OF ASH AND OTHER PYROCLASTICS

106

0

P

200 km

Fig. 2.1. Distribution of the main Quaternary volcanoes (dots) and volcanic ash soils (shaded areas) in Japan. The latter distribution is modified from the data of the Ministry of Agriculture and Forestry (1364).

MlNERALOGY OF VOLCANIC ASH SOILS

107

Egawa et al. (1955), Ishii and Mori (1959), Kanno (1959, 1961), Matsui (1960), Miyazawa (1966), etc. These studies demonstrated that allophane is the dominant constituent of volcanic ash soils, sometimes associated with minor amounts of imogolite, kaolinite, gibbsite, 14 A clay minerals, etc. The amorphous material in weathered pumice was studied by Sudo et al. (1952), Nozawa (1953), Sudo (1953a, 1954), Kuwano and Matsui (1957), Morimoto et al. (1957), Kanno (1959), Matsui (1960), etc., and it was also shown to be allophane. These allophanes were identified mainly on the basis of the absence of sharp reflections in the X-ray diagrams, and of an endotherm at about 150°C and a n exotherm at about 900°C in differential thermal curves. They can therefore be classified as allophane A of Fieldes (1955). Many electron microscopic studies have been made on these allophanes. Sudo (1954, 1956) showed that the allophanes in the volcanic ash soils and weathered pumices consisted of aggregates of fine particles 100-200 A in diameter. Morimoto et al. (1957) and Egawa and Watanabe (1964) made similar observations. Kitagawa (1 971) concluded that the allophane in the weathered pumices consists of hollow spherical particles about 55 A in diameter, and Henmi and Wada (1976) recently arrived at a similar conclusion for the allophane in various volcanic ash soils and weathered pumices. The chemical analytical data for allophane compiled by Ossaka (1960) show(ed that the SiOz/AIZ03 molar ratio for soil allophane falls between 1.0 and 2.5, and that the HsO( *)/A1203 molar ratio is approximately 5. Chemical analyses of allophanes purified from volcanic ash soils and weathered pumices were made by Yoshinaga (1966). These gave SiOz = 31-40%, A1203 = 35-42%, loss on ignition = 16-19%, and SiO2/AIz03molar ratio = 1.3-2.0. Further details of the mineralogical properties of allophane are given in Chapter 4. From a comparison of the chemical compositions of allophane and the original volcanic ash, it is evident that for allophane to be formed, bases and a considerable part of the silica in the volcanic ash must be leached out. Sudo (1953a) regarded allophane as a product of weathering under leaching conditions. Aoniine (1958), after reviewing the literature on allophane, concluded that rapid leaching from fine-grained, porous volcanic ash under almost neutral conditions resulted in the formation of an amorphous colloid with a low SiOz/AL03 ratio, i.e. allophane. Kanno (1961) expressed the same opinion and suggested that rapid desilication is essential for the formation of large amounts of allophane. 2.1.2. Opaline silica Fieldes (1 955) demonstrated the presence of discrete amorphous silica, which he called allophane B, at an early stage in the weathering of volcanic ash in New Zealand. This mineral is characterized by the absence of the 900°C exotherm in the differential thermal curve and the presence of an absorption band at about 800 cm-1 in the infrared spectrum.

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WEATHERING OF ASH AND OTHER PYROCLASTICS

Kanno (1959) examined volcanic ash soils from Hokkaido which were younger than 500 yr B.P., and found that the amorphous material in them showed only a faint exotherm at about 900°C. Egawa and Sat0 (1960) reported that amorphous material in young volcanic ash soils from Hokkaido and northeastern Honshu did not show the exotherm. On the other hand, Miyauchi and Aomine (1964) doubted the presence of allophane B in Japanese volcanic ash soils, since the amorphous material in the young volcanic ash soils which they examined did show the 900°C exotherm, and contained cristobalite to which the observed 800 cm-I band could be attributed. Uchiyama, Masui and Shoji have made important contributions to this problem. Uchiyama et al. (1968a,b) examined the composition of 0.5 N NaOH soluble fractions of soils from Hokkaido derived from volcanic ash or pumice dated at less than 1150 yr B.P. They showed that the SiOZ/Al2O3molar ratios were I .5-25, with average values of 10.3 for soils younger than 500 yr and 5.0 for soils 500-1,150 yr old. The former soils did not show the 900°C exotherm. Shoji and Masui (1969a,b) reexamined two of the young soils (218 and ca. 220 yr old) examined by Uchiyama et al. (1968a,b), and concluded that discrete amorphous silica was present on the basis of a high NaOH soluble SiO2/Al2O3 ratio and the presence of a silica band in the infrared spectrum for < 0.2 pm fractions which contained neither quartz nor cristobalite. They showed by electron microscopy that most of the amorphous silica in the coarser fraction occurred in the form of opaline silica of disc-like shape, with diameters of 0.2-1 5 pm. Later, such opaline silica was identified in many soils from various parts of Japan (Shoji and Masui, 1971; Masui and Shoji, 1975; Tokashiki and Wada, 1975). It was shown to be abundant in the A horizon, a fact suggesting that it may have formed by supersaturation of silica on evaporation. The consumption of aluminum to form humus-aluminum complex suggested by Wada and Harward (1974) and by Tokashiki and Wada (1975) may also contribute to the formation of opaline silica in the A horizon. Shoji and Masui (1972) further examined the < 0.1 pm fraction of young volcanic ash soils from Hokkaido, and showed that the A horizon of soils younger than 1000 yr contains a siliceous amorphous material, opaline silica, and smectite, whereas that of soils older than 1000 yr is composed mainly of smectite. In the case of the B and C horizons, on the other hand, a silica-rich mineralogy similar to the A horizon of the younger soils is replaced by allophane with increasing age. 2.1.3. lmogalite

Shioiri (1935) found white gel-like films in a pumice bed at Kitakami, Iwate Prefecture, and considered them to be composed of allophane. Kuwano and Matsui (1957) examined a similar filmy substance from pumice beds in Tochigi Prefecture, and concluded that it represented a transitional stage from allophane

MINERALOGY OF VOLCANIC ASH SOILS

109

to a crystalline clay mineral. Kanno et al. (1960) also examined similar material from pumice beds at Kitakami and in Tochigi Prefecture, but concluded that it was a mixture of poorly ordered smectite, allophane, and free A1 and Fe compounds. Aomine and Yoshinaga (1955) reported hair-like particles in volcanic ash soils rich in allophane. These studies were a prelude to the finding and establishment of the new mineral “imogolite” by Yoshinaga and Aomine (1962a,b). These workers noticed that some volcanic ash soils contained two kinds of mineral colloid. After dispersing the first, allophane, in an alkaline medium, they succeeded in collecting the second, to which they gave the name imogolite after the name of a glass-rich soil (Imogo) around Hitoyoshi, Kumamoto Prefecture, from which one of their samples was obtained. This material shows broad, but distinct reflections at about 17.7, 12.6, 7.8, 5.6 A, etc. in X-ray diagrams, and an intense endotherm at 170-190°C, an endotherm at about 435”C, and a sharp exotherm at 935-955°C on differential thermal curves. It has a characteristic morphology, viz. a thread-like shape with a cross-sectional diameter of 100-200 A. The molar ratio of SiOz:A1203: Hz0( A) is approximately 1:1:5. Based on these properties, it was considered to be new, and this assessment was approved by the Nomenclature Committee of the Association Internationale pour I‘Etude des Argiles in 1969. A discussion of the structure of imogolite is given in Chapter 4. The occurrence of imogolite in various volcanic ash soils from different parts of Japan was reported by Aomine and Miyauchi (1965), Kawasaki and Aomine (1966), Kanno et al. (1968), Wada and Tokashiki (1972), Shoji and Masui (1972), Aomine and Mizota (1973), and Tokashiki and Wada (1975). The youngest example was that reported in an ash deposit ejected from the Sakurajima volcano in A.D. 1914 (Yoshinaga, 1975). The imogolite in these volcanic ash soils is usually associated with allophane and sometimes with gibbsite (Yoshinaga, 1970; Aomine and Mizota, 1973). The gel-like films in pumice beds were reexamined by Miyauchi and Aomine (1966), Yoshinaga (1968), Wada and Matsubara (1968), Yoshinaga and Yamaguchi (1970), Tazaki (1971), Tazaki and Saji (1972), and Aomine and Mizota (1973). As a result, it was shown that they consist of imogolite, and that, in many of the pumice beds, the imogolite is closely associated with gibbsite. The pumice grains are composed of allophane. In both forms of occurrence, imogolite disappears at great depths, and halloysite which is regarded as a product of resilication (see section 2.2.3) appears instead (Yoshinaga and Yamaguchi, 1970; Yoshinaga, 1970; Aomine and Mizota, 1973). This fact, as well as the close association of imogolite and gibbsite, suggests that the imogolite was formed in an Al-rich environment. The imogolite in volcanic ash soils may have been formed by dedication of allophane or unweathered ash (Yoshinaga, 1970; Wada and Aomine, 1973), and the imogolite occurring as gel-like films in pumice beds may have been formed by precipita-

110

WEATHERING OF ASH AND OTHER PYROCLASTICS

tion of the alumina with silica leached out from pumice grains (Yoshinaga, 1970; Aomine and Mizota, 1973). 2.1.4. 14A Clay minerals Expandable 2 :1 layer silicates and their intergrades to chlorite are important among the crystalline constituents of volcanic ash soils. However, in some cases, they do not originate from weathering. Kanno et al. (1961) reported the presence of smectite and other 14 A clay minerals in ash from a crater of the Kirishima volcano, southern Kyushu, examined immediately after deposition, and concluded that these clay minerals had formed by alteration which occurred in the crater lake before eruption. Kondo (1963) also reported the occurrence of smectite-bearing volcanic ashes around the Usu volcano, Hokkaido, which he thought to be secondary ashes similar to that at Kirishima. Abundant evidence exists to show that 14 A clay minerals are formed by the weathering of volcanic ash. Uchiyama et al. (1962) reported that smectite is the dominant clay mineral in dacitic volcanic ash soils at Kawatabi, Miyagi Prefecture. These soils were later reexamined by Masui et al. (1973), who showed that the dominant mineral is a 14 A mineral with hydroxy-A1 interlayers. Matsui (1963) showed that dacitic volcanic ash soils in the Shimokita Peninsula, Aomori Prefecture, contained 14A clay minerals as minor constituents. Kawasaki and Aomine (1966) reported the occurrence of vermiculite and other 14 8, minerals, in addition to the predominant allophane, in four volcanic ash soils. Masui et al. (1966) examined 10 soil profiles in northeastern Honshu, and found that the <1 ,um fraction of soils with a relatively large clay content is rich in 2:l clay minerals, whereas that of soils with a smaller clay content consists mainly of allophane. The 2:l clay minerals show 14 and 10 A reflections: the 14 8, mineral in the deeper horizons and in soils with a smaller clay content is smectite, whereas that in the surface horizon and in soils with a larger clay content is smectite-chlorite intergrades and vermiculite-chlorite intergrades. Uchiyama et al. (1968c,d,e) and Masui and Shoji (1975) then examined young soils derived from volcanic ash or pumice in Hokkaido, and showed that they contained 14 clay minerals and minor amounts of illite and kaolinite together with the amorphous materials described above. The 14 8, minerals are a mixture of vermiculite and smectite and contain hydroxy-A1interlayers when the soils are well-drained. Chemical analysis of a purified sample revealed that the mineral mixture without Al-interlayering can be expressed as (Si~.ooAll.oo) (A13 osFe3+o.51Fe2+o.osMgo.48)020(0H)4~X1~26. The amount of 14 A minerals constitutes at most about 5 % of the soils dried at 110°C: it is larger in the A horizon than in the deeper horizons. Masui and Shoji (1969a) also showed a predominance of 14 8, minerals among crystalline clay minerals in volcanic ash soils from various localities and in glass fragments in their sand fractions. Examples of X-ray diagrams and electron micrographs of 14 A minerals are shown in Figs. 2.2 and 2.3.

MINERALOGY OF VOLCANIC ASH SOILS Iwaki

lwate

Chokai 14

14

14

u 5'

111

1 0"

U 5"

U 1 0"

u 5'

lo'

Fig. 2.2. X-ray diagrams of volcanic ash soils rich in 2:l clay minerals. The < 1 pm fraction was deferrated, treated_ with _0.5 N NaOH and then glycolated. Horizon Depth -_ ____ - Locality Left Iwate volcano, lwate Prefecture 1 A 15 cm 2 A 45 cm 3 C 95 cm 4 D 120 cm 5 A 15 cm Middle Iwaki volcano, Aoniori Prefecture 6 A 35 cm 7 C 95 cm 8 A 10 cm Right Chokai volcano, Yamagata Prefecture 9 A 20 cm 10 B 35 cm 11 C 75 cm {After Masui, Shoji and Uchiyama, 1966.)

The occurrence of 14 A clay minerals has been reported by Matsui (1969), Matsui et a]. (1970), and Matsui and Saito (1971a) in volcanic ash soils from the Zao volcano, from northern Kyushu, and from the Ashitaka volcano, respectively. They consist of vermiculite-chlorite intergrades and are associated with kaolinite and gibbsite. Wada and Tokashjki (1972) and Tokashiki and Wada (1975) have demonstrated the Occurrence of vermiculite-chlorite intergrades, smectite, vermiculite, and chlorite at several localities in Kyushu.

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WEATHERlNG OF ASH A N D OTHER PYROCLASTICS

______^

-

Fig. 2.3. Electron micrographs of volcanic ash soils rich in 2:l clay minerals. A, Kawatabi, Miyagi Prefecture, top soil, < 0.2 pm fraction. B, Kitakami, Iwate Prefecture, top soil, < 0.2 pm fraction. The scale-lines represent 0.5 pm (By courtesy of S. Shoji and M. Saigusa.)

MINERALOGY OF VOLCANIC ASH SOILS

113

These occurrences of 14 A clay minerals apparently indicate that they were formed by weathering. Kawasaki and Aomine (1966) considered that the 14 A minerals in their four volcanic ash soils were, at least in part, alteration products of mica, amphibole, or pyroxene. Wada and Aomine (1973) and Tokashiki and Wada (1975) noted that 14 A minerals were abundant in weathered dacitic ash and, on this basis, the former authors concluded them to be inherited from mica or hornblende in the parent ash. In the parent ashes of the soils described here, however, no mica or only very small amounts of mica were actually found. It seems improbable therefore that a major part of the 14 A minerals represents alteration products from mica. As shown by Masui and Shoji (1967, 1969a, 1970), the 14 minerals can be formed from volcanic glass :it must therefore have been derived from various constituents of volcanic ash. The soils in which 14 A minerals were reported by Uchiyama et al. (1968c, d,e) and Masui and Shoji (1969a, 1975), contained silica-rich amorphous materials like the opaline silica described above. This suggests that the 14 L% minerals may be weathering products of a siliceous environment, for which an acidic parent ash or accumulation of humus may be responsible. These minerals must have begun to form at a very early stage of weathering and, as will be described in section 2.2. persisted for a long period. As shown by Uchiyama et al. (1968d) and Masui and Shoji (1969a), smectite is apparently transformed to vermiculitechlorite intergrades with the progress of weathering, since the latter are more abundant in older ashes and in the surface horizon. 2.1.5. Other minerals

Kaolin minerals represent another important constituent of volcanic ash soils, and are especially common in acid soils derived from andesitic or dacitic ash (Kanno, 1961; Miyazawa, 1966). Usually they consist of platy kaolinite, although very small amounts of halloysite have occasionally been detected under the electron microscope (Masui and Shoji, 1969a,b). Halloysite occurs in volcanic ashes and pumices of older ages as described in section 2.2, and is therefore found at greater depths unless the overlying pyroclastic deposits have been removed by erosion. Gibbsite has often been reported from volcanic ash soils. Sometimes it is associated with allophane and imogolite, and in certain other cases it is associated with allophane, vermiculite-chlorite intergrades, and kaolinite. Kanno (196 1) considered that gibbsite was formed in acid soils by the leaching of aluminum from allophane. Miyazawa (1966) showed that gibbsite tends to be more abundant in the upper part of the B horizon and in soils poor in unaltered glass, and concluded that it was formed by dedication of allophane. Illite and chlorite are also found in volcanic ash soils, but they are neither abundant nor wid ely distributed .

WEATHERING OF ASH AND OTHER PYROCLASTICS

114

2.2. DEEP WEATHERING OF PYROCLASTIC DEPOSITS

Repeated falls of volcanic ash, pumice, and scoria on the land have led to the formation of piles of pyroclastic deposits in many areas of Japan. In addition to the near-surface weathering of these pyroclastic deposits described above, alteration has also taken place in their deeply buried parts. Many studies have been made on the mineralogical properties of Quaternary pyroclastic deposits since 1954, when Sudo (1954) demonstrated that the upper part of pyroclastic deposits in the Kanto district is composed of allophane, whereas the lower part is composed of halloysite. 2.2.1. Mineralogy of pyroclastic deposits in the Kanto district

Quaternary pyroclastic deposits are extensively developed on terraces and hills in the Kanto district. They are derived from volcanoes lying to the west of this district, e.g. Fuji, Hakone, Asama, Haruna, Akagi, and Nantai, and are mainly composed of volcanic ash associated with pumice and scoria layers. The volcanic ash has generally been altered to brown clayey material which is customarily termed “Kanto Loam”. Pleistocene sediments occur extensively in the Kanto Plain and form terraces at various levels. The terraces are covered by pyroclastic deposits, which are thicker on the higher-level (older) terraces. As shown in Fig. 2.4, the pyroclastic deposits around Tokyo may be divided into the following loam formations on the basis of their relation to the terraces at different levels. Tachikawa Loam -ca. 30,000 yr Be.*Musashino Loam -a.60,000 yr B.P.*Shimosueyoshi Loam -Riss/Wurm interglacialTama Loam

Thickness 2 4m

Mafic minerals Olivine > hypersthene > augite

3-5 m

Olivine, hypersthene, augite

2-7 m

Small in amount; weathered olivine in the upper part and hornblende in the lower part

< 30 rn

Hornblende, magnetite

*After Machida (1971). Tachikawa Loam

..

Formation

Shirnosueyoshi Formation

Grave’

Tachikawa Gravel

,/

Alluvium

Fig. 2.4. Schematic cross-section showing the relationship between the terraces and pyroclastic deposits around Tokyo.

DEEP WEATHERING OF PYROCLASTICS

11.5

The boundaries between these formations have been defined by the presence of paleosols or zones rich in cracks, and by unconformable relations at the terrace edges. Following the work of Sudo (1954) and Kanno and Kuwano (1957), Tsuchiya and Kurabayashi (1958) and Kurabayashi and Tsuchiya (1959) made extensive studies of the mineral composition of the Quaternary pyroclastic deposits around Tokyo. According to them, the Tachikawa Loam is usually composed of allophane, while the Musashino Loam is rich in halloysite, although many samples still contain allophane. The Shimosueyoshi and Tama Loams, on the other hand, are composed mainly of halloysite, which, in many places, exists in a partially dehydrated state. Thus, halloysite in general takes the place of allophane with increasing depth (Fig. 2.5). Pumice beds intercalated with these loams are also altered, but they seem to be more resistant to such changes. For example, the Tokyo Pumice intercalated in the lower part of the Musashino Loam to the east of Tokyo is composed of allophane. On the other hand, buried humic soils intercalatedwith the loams appear to be more liable to undergo such alteration; for example, two buried soils in the Tachikawa Loam and those at the top of the Musashino and the Shjmosueyoshi Loams are rich in halloysite (Tsuchiya and Kurabayashi, 1958;Kurabayashi and Tsuchiya, 1959;Matsui and Saito, 1971b). The partially dehydrated halloysite is characterized by a poorly defined basal reflection between 7 and 10 A,and tends to occur in the upper part of volcanic ashes of marine deposition (Tsuchiya and Kurahayashi, 1958; Kurabayashi and Tsuchiya, 1962). Kurabayashi and Tsuchiya (1965) examined the minor constituents of allophane-rich samples of the l o a m after removing allophane by NaOH treatment (Hashimoto and Jackson, 1960). Their results showed that the upper part of the Kanto Loam usually contains 14 A minerals, which they considered to be vermiculite-chlorite intergrades and chlorite. Pumice, on the other hand, is usually free from 14 8, minerals. Mineralogical studies of the pyroclastic deposits in the northern part of the Kanto district were made by Nozawa (1953), Kuwano and Matsui (1957), Morimot0 et al. (1957), Matsui (1960), Kurabayashi and Tsuchiya (1961b), etc. The general tendency for halloysite to replace allophane at increasing depth also holds true in this region. The area around Utsunomiya, Tochigi Prefecture, is known for its abundant occurrence of pumice beds, among which the upper three, the Shichihonzakura Pumice, Imaichi Pumice, and Kanuma Pumice in descending order, are composed of allophane sometimes associated with gellike films of imogolite. These beds have attracted the attention of many clay mineralogists. In some places, the Kanuma Pumice has been altered to white halloysite clay (see section 2.2.5).

WEATHERING OF ASH AND OTHER PYROCLASTICS

116

Halloysite

En/Ex

0.0

100%

5.0

1.

Tachikawa Loam

___-

R

ox

Musashino Loam

X.

__--

%

01

.

x X X X

X X

X X

0

Tama Loam

C

0

C

0 0

0

C

0

C

0

0

I7

Loam' Dark-colored part Weathered pumice

X

0

Fig. 2.5. Estimation of the amount of halloysite in the < 2 pm fractions of pyroclastic deposits around Tokyo. Left : Columnar sections of pyroclastic deposits from which samples were taken: A, Okamoto, Tokyo Prefecture; B, Chitose, Kanagawa Prefecture; C, Oshinuma, Kanagawa Prefecture. Middle: ratio of the peak area of the 550°C endotherm to that of the 950°C exotherm in the differential thermal curve. Right : amount of halloysite estimated from the peak area of the 10 A reSample from column A flection in the X-ray diagram. Sample from column B (After Kurabayashi and Tsuchiya, (1961a.) Sample from column C

2.2.2. Mineralogy of pyroclastic deposits in areas outside the Kanto district In Hokkaido, there are many active volcanoes which have ejected young pyroclastic materials. Ishii and Kondo (1963) and Ishii (1963) have reported the same tendency as in the Kanto district, i.e. the upper part of the pyroclastic deposits is composed of allophane, whereas the lower part is composed of halloysite. Here, however, the transition from halloysite to allophane occurs at an age of about 9,000 yr B.P., since the pumice fall deposit from the Eniwa

DEEP WEATHERING OF PYROCLASTICS

117

volcano (En a), which is a little older than 9,000 yr B.P. according to Sasaki et al. (1971), contains halloysiie. In the pyroclastic deposits around Hachinohe, Aomori Prefecture, and Kuji, Iwate Prefecture, a similar relation has been reported by Kurabayashi and Tsuchiya (1967), although the upper part of the pyroclastic deposits which correspond to 1he Musashino and Shimosueyoshi Loams in the Kanto district consists mainly of interstratified mica/smectite with the basal reflection at about 11 A. The pyroclastic deposits to the east of the Yatsugatake volcano, Nagano Prefecture, have been examined by Kurabayashi (1975). The results were similar to those in the Kanto district, except that (1) the top of the pyroclastic deposits consists of vermiculite-chlorite intergrades and gibbsite, and (2) pyroclastics older than the Tama Loam, consisting of halloysite, smectite, etc., are found. Kurabayashi and Tsuchiya (1967) have examined the pyroclastic deposits around Shiojiri and Ina, Nagano Prefecture, and showed that they also display a similar relation to those in the Kanto district. A considerable amount of vermiculite-chlorite intergrades is contained in the upper part of the youngest deposits, the Upper Loam, which otherwise consist of allophane. The underlying Middle Loam which is composed of allophane and halloysite contains many pumice layers, among which Pm-I derived from the Ontake volcano is a good time marker extending to the Kanto district far to the east, where it i s intercalated with the Shimosueyoshi Loam. The Pm-I pumice is composed of allophane, which has in part been further altered to halloysite (Nagasawa et al., 1969; Watanabe, 1972). The pyroclastic deposits at the foot of the Ashitaka volcano, Shizuoka Prefecture, have been examined by Matsui and Saito (1971a). The results showed that the clay fraction of the Upper Loam is composed mainly of vermiculitechlorite intergrades and kaolinite, in contrast to the Middle and Lower Loams where allophane is dominant. The pyroclastic deposits derived from the Daisen volcano, Tottori Prefecture, have been examined by Kurabayashi (1972) and Tazaki (1972). Allophane is abundant in some samples of the Upper Volcanic Ash and a pumice bed intercalated in the Middle Volcanic Ash, and halloysite is present in some samples of the Middle and Lower Volcanic Ashes. The most important character of the pyroclastics in this area, however, is the abundance of 14 8, minerals and illite in the volcanic ashes. The 14 A minerals are considered to be vermiculitechlorite intergrades, sometimes associated with minor amounts of chlorite. The 14 A minerals and illite show sharper basal reflections in X-ray diagrams than those formed by the weathering of volcanic ash described in section 2.1.4. Based on this fact, as well as their distribution and the similarity to the loess in western Japan and China, Kurabayashi (1972) considered these materials to be, or to be derived from, foreign materials transported by the wind and mixed with the volcanic ash. The pyroclastic deposits derived from the Sambesan volcano,

118

WEATHERING OF ASH AND OTHER PYROCLASTICS

Shimane Prefecture, examined by Tazaki (1972) are similar to those of Daisen, although they are richer in pumice fall deposits. 2.2.3. Transformation of allophane to halloysite

All of the examples mentioned above, except Ashitaka, indicate that younger pyroclastics tend to consist of allophane, whereas older pyroclastics consist of halloysite. This fact suggests that allophane originally formed by weathering has been transformed into halloysite with age. However, the age at which the transformation occurred is different among volcanic ash, pumice, and buried soil, as shown by the pyroclastic deposits around Tokyo (section 2.2.1). Further, as pointed out first by Miyazawa (1966), the pyroclastic deposits of different areas show different ages for this transformation. The age of transformation is about 30,000 yr B.P. in the vicinity of Tokyo, and similar values hold around Hachinohe and Kuji and around Shiojiri and h a . On the other hand, it is about 9000 yr B.P. in Hokkaido and 8000-9000 yr B.P. in the Aso volcano area, Kyushu (Aomine and Miyauchi, 1963).These facts indicate that the transformation of allophane into halloysite is not a crystallization reaction which can be expressed simply as a function of time. Masui and Shoji (1969~)expressed the same view on the basis of their observation that halloysite usually appears suddenly at a certain depth. Further evidence for this conclusion comes from the pumice in the Atsuta Formation of the Nagoya area, Aiclii Prefecture. This formation consists of marine sediments dating from the Riss/Wurm interglacial and is composed mainly of sand. It has been upheaved and now consititutes coastal terraces. Pumice grains are disseminated in the sand. Although no broad, systematic studies have been made on the mineralogy of the pumice due to the urbanization of the area, the present author’s results (Nagasawa, unpublished) show that the pumice contained in the superficial part of the Atsuta terraces is composed of allophane, whereas that in deeper parts is composed of halloysite (Fig. 2.6). The pumice in the much deeper parts of the Atsuta Formation remains fresh. Since alteration of the pumice composed of allophane and that composed of halloysite into the respective minerals began at almost the same time, i.e. the time of upheaval, the different courses of alteration must be attributed to differences in environment after this time. Kanno (1961) considered the transformation of allophane to halloysite in the deeper portion of thick pyroclastic deposits to be due to the addition of silica by percolating water which carried silica as a result of desilication of the overlying portion of the pyroclastics. The work of Yamada et al. (1969) and Aomine and Mizota (1973) is of significance in this respect. They examined the pyroclastic deposits around Utsunomiya and noticed a variation in mineral composition within materials in a volcanic ash bed of the same age. The uppermost part of the pyroclastics in this area, the Shichihonzakura Pumice and the Imaichi Pumice, which both derive from the Nantai volcano, is distributed only

D E E P W E A T H E R I NG OF PYROCLASTICS

119

Fig. 2.6. Electron micrographs of weathered pumice contained in sand of the Atsuta formation (Nagoya, Aichi Prefecture). A, Weathered pumice from the superficial part of the Atsuta terrace. B, Weathered pumice taken at a depth of about 4.5 m from the terrace surface. The scale-lines represent, 0.5 pm.

in the northern part of the area. A volcanic ash bed underlies the Imaichi Pumice, and then comes the Kanuma Pumice. Both beds are distributed throughout this area. The volcanic ash overlying the Kanuma Pumice is composed of halloysite associated with allophane and vermiculite, when it is covered by the Shichihonzakura and Imaichi Pumices. On the other hand, it is composed of allophane associated with imogolite, gibbsite, and vermiculite-chlorite intergrades, when it has no overburden. These findings support Kanno’s reasoning and indicate that the formation of allophane in the upper part and the transformation of allophane into halloysite in the lower part are coupled chemical reactions. 2.2.4. Morphology of allophane and halloysite

Numerous electron micrographs of allophane and halloysite have been published in papers concerned with the clay minerals of Quaternary pyroclastic deposits. Based on electron micrographs for the pyroclastics of the Kanto district, Sudo (1954, 1956) concluded that fine particles, 0.01-0.02 ,urn in diameter, of allophane coagulate to form rounded grains about 0.1 ,um in diameter, which are then modified into aggregates of extremely fine, fibrous crystals of halloysite. With the progress of crystallization, some of the fibrous crystals grow as projections from the rounded grains, and finally the rounded grains are entirely changed into relatively large, elongate crystals of halloysite.

120

WEATHERING OF ASH AND OTHER PYROCLASTICS

Fig. 2.7. Electron micrographs illustrating Kurabayashi-Tsuchiya’sclassification of the morphology of allophane and halloysite in wealhercd pyroclastics. A, Osakada, near Shiojiri, Nagano Prefecture, morphology A. B, Osakada, morphology B1. C , Ashikaga, Tochigi Prefecture, morphology Ba. D,

DEEP WEATHERING OF PYROCLASTICS

121

Osawashinden, Nagano Prefecture, morphology C1. E, Osawashinden, morphology Cz; F, Akasaka, near Utsunomiya, Tochigi Prefecture, morphology D. G, Inage, Chiba Prefecture, morphology El. H, Matsudo, Chiba Prefecture, morphology Ez. The scale-lines represent 0.5 pm. (By courtesy of S . Kurabayashi and T. Tsuchiya.)

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WEATHERING OF ASH A N D OTHER PYROCLASTICS

Kurabayashi and Tsuchiya (1960) made a morphological study of clay particles from the pyroclastics of the Kanto district. They divided the morphology of the clay particles into the following types. A: aggregates of fine particles about 0.05 pm in diameter; these are composed of allophane. B1: aggregates of fine particles like A but associated with minor amounts of spherical particles about 0.2 pm in diameter; these consist of allophane and halloysite. Bz: spherical particles and tubular particles, the latter either projecting from the former or forming particles separate from them; these consist of halloysite. C1: tubes about 0.2 pm in length plus minor amounts of spherical particles; these consist of halloysite. CZ: tubular particles about 0.2 pm in length which consist of halloysite. D : tubular particles longer than 0.2 pm in length which consist of halloysite. El: tubes, spherical particles about 0.1 pm in diameter, and plates; these consist of partially dehydrated halloysite. Ez: partly unrolled tubes and plates; these consist of partially dehydrated halloysite. The Tachikawa Loam is composed of clays with morphologies A and BI, the Masashino Loam has morphologies B1 and Be, the Shimosueyoshi Loam CI, CZ,D1, El and Ez, and the Tama Loam Bz, D, El and Ez. The general course of morphological change was thus concluded to be A + B -+C 4D and C,D -+ E. Electron micrographs illustrating the above morphologies are shown in Fig. 2.7, although some samples derive from areas other than the Kanto district. The fact that some halloysites have a spherical shape was established by Sudo (1953b) and Sudo and Takahashi (1956) in Japanese clays. In fact, the halloysite of Quaternary pyroclastics provided many examples of such spherical morphology. Descriptions on the detailed morphology of allophane and halloysite are given in Chapters 4 and 5, respectively. 2.2.5.

Formation of white clay composed of halloysite

White clay is often found in the lower part of pyroclastic deposits. It is composed of halloysite, and is characterized by its white color in contrast to the brown color of the altered volcanic ash or so-called loam mentioned above. Kanno (1959) reported that a layer of white halloysite clay about 5 mm thick and accompanied by a concentration of Mn at its base, occurs at the bottom of the yellow Kanuma Pumice composed of allophane at Kanuma, Tochigi Prefecture. He considered this clay to have been formed by the action of percolating water. The Kanuma Pumice is entirely altered to white halloysite clay near Imaichi (Kuwano and Matsui, 1957; Morimoto et al., 1957), and is partially altered to form patches of halloysite clay in other areas (Aomine and Mizota, 1973). Similar examples of white halloysite clay formation from allophane in pumice beds have been reported from the vicinity of Ina, Nagano Prefecture

REFERENCES

123

(Nagasawa et al., 1969; Watanabe, 1972) and Yame and other places in Kyushu (Kinoshita and Muchi, 1954). Yoshinaga et al. (1973) have also reported an accumulation of halloysite and gibbsite at the bottom of the Kitakami Pumice composed of allophane near Kitakami, Iwate Prefecture. Aomine and Wada (1962) made an important contribution to this problem. They discovered veins of white halloysite clay in volcanic ash, and patches and blocks of white halloysite clay in pumice, both in the deeper part of the pyroclastics of the Aso volcano, Kyushu. The volcanic ash and pumice are composed of allophane. Also, as at Kanuma, the white clay is accompanied by black Mn concretions. They considered that repeated replenishment of fresh water was responsible for the formation of the white clay on the basis of chemical analysis of bulk samples which showed a loss of SiOz and bases. This view is also supported by the fact that a similar white clay composed of halloysite is known to have been formed from fresh volcanic glass instead of allophane. The present author (Nagasawa and Tsuzuki, 1976) has shown that the lower part of a bed of transported pumice of Pliocene age around Nagoya was altered to white halloysite clay, and considered the change to have been due to the action of circulating ground water. Tomita and Onishi (1976) have also reported the formation of white halloysite clay at the basal part of the “Shirasu” non-welded pumice flow deposits in Kagoshima Prefecture, and attributed it to ground water permeating the Shirasu. REFERENCES Aomine, S. and Yoshinaga, N. (1955) Soil Sci. 79, 349. Aomine, S. (1958) J . Sci. Soil Manure Japan 28, 508. Aomine, S. and Wada, K. (1962) Amer. Miner. 47, 1024. Aomine, S. and Miyauchi, N. (1963) Nature 199, 1311. Aomine, S. and Miyauchi, N. (1965) Soil Sci. Plant Nutr. (Tokyo) 11, 212. Aomine, S. and Mizota, C. (1973) Proc. Intern. Clay Conf. Madrid 1972, 207. Egawa, T., Watanabe, Y . and Sato, A. (1955) Bull. Natl. Inst. Agv. Sci. (Tokyo) B5, 39. Egawa, T. and Sato, A. (1960) Advances in Clay Science, vol. 2, p. 385, Gihodo. Egawa, T. and Watanabe, Y . (1964) Bull. Natl. Inst. Agr. Sci. (Tokyo) B14, 173. Fieldes, M. (1955) New Zea!and J. Sci. Tech. 37B, 336. Hashimoto, I. and Jackson, M. L. (1960) Clays Clay Miner. 7, 102. Henmi, T. and Wada, K. (1976) Amer. Miner. 61, 379. Ishii, J. and Mori, T. (1959) J. Geol. SOC.Japan 65, 357. Ishii, J. (1963) J . Fac. Sci. Hokkaido Univ. Ser. IV, 11, 545. Jshii, J. and Kondo, Y . (1963) Advances in Clay Science, vol. 4, p. 193, Gihodo. Kanno, I. and Kuwano, Y . (1957) Kagaku (Japanese) 27, 253. Kanno, 1. (1959) Advances in Clay Science, vol. 1, p. 213, Gihodo. Kanno, I., Kuwano, Y . and Honjo, Y . (1960) Advances in Clay Science, vol. 2, p. 355, Gihodo. Kanno, I. (1961) Bull. Kyushu Agr. Expt. Sta. 7, 1. Kanno, I., Honjo, Y . and Kuwano, Y . (1961) Advances in Clay Science, vol. 3, p. 214, Gihodo. Kanno, I., Onikura, Y. and Higashi, T. (1968) Trans. 9th Intern. Congr. Soil Sci. Adelaide 1968, 3, 111. Kawamura, K. and Funabiki, S. (1936) J . Sci. Soil Manure Japan 10, 281. Kawasaki, H. and Aomine, S. (1966) Soil Sci. Plant Nurr. (Tokyo) 12, 144.

1 24

WEATHERING OF ASH AND OTHER PYROCLASTICS

Kinoshita, K. and Muchi, M. (1954) J. Mining Inst. Kyushu 22, 279. Kitagawa, Y. (1971) Amer. Miner. 56, 465. Kondo, Y. (1963) J. Geol. SOC.Japan 69, 362. Kurabayashi, S. and Tsuchiya, T. (1959) J. Geol. SOC.Japan 65, 545. Kurabayashi, S. and Tsuchiya, T. (1960) J. Geol. SOC.Japan 66, 586. Kurabayashi, S. and Tsuchiya, T. (1961a) Clay Sci. 1, 15. Kurabayashi, S. and Tsuchiya, T. (1961b) Advances in Clay Science, vol. 3, p. 204, Gihodo. Kurabayashi, S. and Tsuchiya, T. (1962) Earth Sci. No. 60/61, 16. Kurabayashi, S. and Tsuchiya, T. (1965) Advances in Clay Science, vol. 5, p. 19, Gihodo. Kurabayashi, S. and Tsuchiya, T. (1967) Prof. Hidekata Shibata Memorial Volume, 140. Kurabayashi, S. (1972) J. Geol.. SOC.Japan 78, 1. Kurabayashi, S. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 185. Kuwano, Y. and Matsui, T. (1957) Misc. Rept. Res. Inst. Nat. Resources 45, 33. Machida, H. (1971) Quat. Res. 10, 1. Masui, J., Shoji, S. and Uchiyama, N. (1966) Tohoku J. Agr. Res. 17, 17. Masui, J. and Shoji, S. (1967) Pedologist 11, 33. Masui, J. and Shoji, S. (1969a) Proc. Intern. Clay Conf. Tokyo 1969, 1, 383. Masui, J. and Shoji, S. (1969b) J. Sci. Soil Manure Japan 40, 485. Masui, J. and Shoji, S. (1969~)J. Sci. Soil Milnure Japan 40,493. Masui, J. and Shoji, S. (1970) J. Clay Sci.SOC.Jupan 9, (3/4), 29. Masui, J., Shoji, S., Saigusa, M., Ando, H., Kobayashi, S., Yamada, I. and Saito, K. (1973) Tohoku J. kgr. Res. 24, 166. Masui, J. and Shoji, S. (1975) Contributions to C h y Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 192. Matsui, T. (1960) Advances in Clay Science, vol. 2, p . 229, Gihodo. Matsui, T. (1963) Advances in Clay Science, vol. 4, p. 267, Gihodo. Matsui, T. (1969) Misc. Rept. Res. Inst. Nut. Resources 71, 22. Matsui, T., Saito, K. and Yano, Y. (1970) Misc. Rept. Res. Inst. Nat. Resources 73, 37. Matsui, T. and Saito, K. (1971a) Quat. Res. 10, 69. Matsui, T. and Saito, K. (1971b) J. Clay Sci. Soc. Japan 11, 106. Ministry of Agriculture and Forestry (1964) Volcanic Ash Soils in Japm. Miyauchi, N. and Aomine, S. (1964) Soil Sci. Plunt Nutr. (Tokyo) 10, 199. Miyauchi, N. and Aomine, S. (1966) Soil Sci. Plant Nutr. (Tokyo) 12, 187. Miyazawa, K. (1966) Bull, Natl. Inst. Agr. Sci. (Tokyo) B17, 1. Morimoto, R., Ossaka, J. and Fukuda, T. (1957) Bu!I. Earthquake Res. Inst. Univ. Tokyo 35, 359. Nagasawa, K., Takeshi, H., Fujii, N. and Hachisuka, E. (1969) The ClaysofJapan, Geol. Surv. Japan, 17. Nagasawa, K. and Tsuzuki, Y. (1976) Geology of the Seto, Shokozan and Itaya Kaolin Deposits--A Guide to the Field Investigations, 7th Symp. Genesis of Kaolin, 1. Nozawa, K. (1953) Misc. Rept. Res. Inst. Nat. Resources 30, 56. Ossaka, J. (1960) Advances in Clay Science, vol. 2, p. 337, Gihodo. Sasaki, T., Gtayama, M., Tomioka, E., Sasaki, S., Yazawa, M., Yamada,S., Yano, Y. and Kitagawa, Y. (1971) Quat. Res. 10, 117. Shioiri, M. (1935) Nigpon Gakujutsu Kyokai Hokoku (Japanese) 10, 694. Shoji, S. and Masui, J. (1969a) Soif Sci. Plant Nutr. (Tokyo) 15, 161. Shoji, S. and Masui, J. (1969b) Soil Sci. PIant Nutr. (Tokyo) 15, 191. Shoji, S. and Masui, J. (1971) J. Soil Sci. 22, 101. Shoji, S. and Masui, J. (1972) J. Sci. Soil Manure Japan 43, 187. Sudo, T., Nagasawa, K., Amafuji, M., Kimura, M., Honda, S., Muto, T. and Tanemura, M. (1952) J. Geol. SOC.Jupan 58, 115. Sudo, T. (1953a) Compt. Rend. 19e Session, Cli-EA, Congr. GCol. Intern. Alger 1952, 18, 123. Sudo, T. (1953b) Miner. J. 1, 66. Sudo, T. (1954) Cluy Miner. Bull. 2, 96. Sudo, T. (1956) Sci. Rept. Tokyo Kyoiku Daignku Sec. C, 5.39. Sudo, T. and Takahashi, H. (1956) Clays Clay Miner. 4, 67. Tazaki, K. (1971) J. Geol. Soc. Japan 77, 407.

REFERENCES Tazaki, K. (1972) Earth Sci. 26, 1 . Tazaki, K. and Saji, K. (1972) J. Geol. SOC.Japan 78, 627. Tokashiki, Y. and Wada, K. (1975) Geoderma 14, 47. Tornita, K. and Onishi, K. (1976) J . Clay Sci. SOC.Japan 16, 56. Tsuchiya, T. and Kurabayashi, S. (1958) 1. Geol. Soc. Japan 64, 605. Uchiyarna, N., Masui, J. and Onikura, Y. (1962) Soil Sci. Plant Nutr. (Tokyo) 8, 13. Uchiyama, N., Masui, J. and Shoji, S. (1968a) J. Sci. Soil Manure Japan 39, 101. Uchiyama, N., Masui, J. and Shoji, S. (1968b) J . Sci. Soil Manure Japan 39, 149. Uchiyama, N., Masui, J. and Shoji, S. (196%) J. Sci. Soil Manure Japan 39, 154. Uchiyama, N., Masui, J. and Shoji, S. (1968d) Soil Sci. Plant Nutr. (Tokyo) 14, 125. Uchiyama, N., Masui, J. and Shoji, S. (1968e) Soil Sci. Plant Nutr. (Tokyo) 14, 133. Wada, K. and Matsubara, I. (1968) Trans. 9th Intern. Congr. Soil Sci. Adeiaide 1968, 3, 123. Wada, K. and Tokashiki, Y. (1972) Geoderma 7, 199. Wada, K. and Aomine, S. (1973) Soil Sci. 116, 170. Wada, K. and Harward, M. E. (1974) Advan. Agron. 26, 211. Watanabe, K. (1972) Quat. Res. 11, 296. Yamada, H., Iwai, S. and Ossaka, .I.(1969) Proc. Intern. Clay Conf. Tokyo 1969,1, 359. Yoshinaga, N. and Aomine, S. (1962a) Soil Sci. Plant Nutr. (Tokyo) 8, 52. Yoshinaga, N. and Aornine, S. (1962b) Soil Sci. Piant Nutr. (Tokyo) 8, 114. Yoshinaga, N. (1966) Soil Sci. Plant Nutr. (Tokyo) 12,47. Yoshinaga, N. (1968) Soil Sci. Plant Nutr. (Tokyo) 14, 238. Yoshinaga, N. (1970) J . Clay Sci. SOC.Japan 9, (3/4), 1. Yoshinaga, N. and Yarnaguchi, M. (1970) Soil Sci. Plant Nutr. (Tokyo) 16, 215. Yoshinaga, N., Nakai, M. and Yamaguchi, M. (1973) Clay Sci. 4, 155. Yoshinaga, N. (1975) J. Clay Sci. SOC.Japan 15, 65.

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Chapter 3 Wall rock alteration of Kuroko deposits

Haruo SHIROZU

The Kuroko deposits are representative and important metallic ore deposits in Japan. They occur in altered pyroclastics of the Green Tuff regions, and are accompanied by remarkable clay alteration. Recent clay mineralogical and geological studies of the alteration zones in the deposits have revealed the alteration patterns together with the occurrence of numerous clay minerals, their mineralogical nature and distribution in the alteration zones. This Chapter will give an outline of the main findings, together with a brief sketch of the Kuroko deposits themselves. 3.1. KUROKO DEPOSITS

Kuroko deposits are strata-bound polymetallic sulfide-sulfatedeposits genetically related to Miocene felsic volcanism. They usually occur at a particular horizon of the Green Tuff, in which thick formations of green-colored volcanic materials are extensively accumulated. Fig. 3.1 shows the distribution of the Green Tuff and main Kuroko and Kuroko-type deposits, together with the names of the Kuroko areas and mines referred to in this Chapter. The Hokuroku district is the most important Kuroko area. 3.1.1.

General features of fhe Kuroko deposits

The general features of the Kuroko deposits have been described by Matsukuma and Horikoshi (1970), Tatsumi and Watanabe (1971), Sato (1974), Lambert and Sato (1974), etc. An idealized section of a Kuroko deposit is shown in Fig. 3.2, in which the distribution of the principal clay minerals in the alteration zones directly adjacent to or within the ore bodies is also indicated (Shirozu, 1974). The Kuroko deposits are composed of stratiform parts, oval shaped in plan, and stockwork parts underlying the stratiform parts. The stratiform ores are massive but generally show zoning of their constituent minerals, as described later, and the ore bodies are usually enveloped by white clays. The stockwork ores consist of disseminated and network mineralizations distributed in irregular funnel-shape zones in silicified felsic lavas (called white rhyolite) and pyro127

WALL ROCK ALTERATION OF KUROKO DEPOSITS

128

Green Tuff Region o

Kuroko deposits Kuroko-type stockwork deposits

d.

Kuroko-type gypsum deposits

Hanaoka. Shakanai

HOKUROKU DISTRICT

SEA OF JAPAN

NISHI-AIZU DISTRICT

PACIFIC OCEAN

-

0

100

200km

Fig. 3.1. Distribution of Kuroko mines in Japan.

m 1m 2m 3m 4m 5m 6a

7 1”,”18 ”9

~

l

o

~

l

l

~

1

Fig.3.2. Idealized section of a Kuroko deposit, showing the distribution of the principal clay minerals (Shirozu, 1974). 1, Silicified rock; 2, siliceous ore; 3, gypsum ore; 4, yellow ore; 5, black ore; 6, ferruginous chert; 7, dioctahedral mica; 8, interstratified dioctahedral mica/montmorillonite having small amounts of montmorillonite layers; 9, interstratified dioctahedral mica/montmorillonite with abundant montmorillonite layers; 10, FeMg-chlorite; 11, Mg-chlorite; 12, interstratified Mg-chlorite/ saponite

2

KUROKO DEPOSITS

129

clastics. Lenticular or irregular masses of gypsum and/or anhydrite also occur in the low horizons in most cases. Thin beds or small lenses of ferruginous chert are often present either directly overlying the stratiform ore body or within the hanging wall clays. Typical Kuroko deposits are characterized by the following distinct vertical zoning of their constituents, from the base to top. Footwall: silicified rhyolite and pyroclastic rocks. Below the central part of the ore deposit, the rocks are disseminated and veined by sulfides. Gypsum ore : gypsum-anhydrite-pyrite-clay ore. Lenticular or irregular masses. This ore also often occurs in the upper horizon. Siliceous ore: Cu-bearing siliceous stockwork ore. Pyrite ore : monomineralic pyrite ore. Usually stratiform. Yellow ore: pyrite-chalcopyrite stratiform ore. Black ore: sphalerite-galena-chalcopyrite-pyrite-baritestratiform ore, containing tetrahedrite, tennantite, bornite, Ag-bearing minerals, electrum, sulfosalt minerals, etc. Barite ore: monomineralic barite stratiform ore. Ferruginous chert: a thin bed of hematite and quartz. Hanging wall: argillized tuff and mudstone. White clays are frequently intercalated between these ore zones, and the ores sometimes contain considerable amounts of clay. The stratigraphical succession corresponds well to the sequence of mineralization. The relative abundances of the different zones vary from deposit to deposit, and in many cases one or more zones may be lacking. It is not uncommon that the stratiform ore body is very small or absent above a productive stockwork ore body, or that only a trace of sulfide mineralization is observed in and adjacent to a large gypsum ore body. The former is called a Kuroko-type stockwork deposit, and the latter a Kuroko-type gypsum deposit. 3.1.2. Genesis of Kuroko deposits

Recent geological and geochemical data on many Kuroko deposits have led to almost unanimous agreement among Japanese geologists concerning the general processes involved in their formation. That is to say, the Kuroko deposits are considered to have formed in middle Miocene sedimentary basins with close genetic relations to submarine felsic volcanic activity. In other words, they are of submarine exhalative or volcanic-sedimentary origin. The stockwork type mineralization is believed to have occurred epigenetically as a result of upward movement of hydrothermal fluids through brecciated lava domes, and the overlying bedded mineralization is considered to have taken place syngenetically where these ore fluids emanated at the submarine surface (Tatsumi and Watanabe, 1971; Lambert and Sato, 1974). The ore formation temperatures estimated from data on fluid inclusions,

WALL ROCK ALTERATION OF KUROKO DEPOSITS

130

sulfur isotopes, etc. lie in the range 100 to 250”C, possibly up to 300°C at maxi-

mum. Of these, the higher temperatures apply to stockwork ores and the lower ones to stratiform ores (Tokunaga and Honma, 1974; Lambert and Sato, 1974) 3.2.

ALTERATION PATTERNS

Since Iwao et al. (1954) and Sudo (1954) first recognized the zonal distribution of altered wall rocks in the Motoyama deposit of the Kosaka mine and in the Nishikannodo deposit of the Hanaoka mine, respectively, a large amount of data on the wall rock alteration of Kuroko deposits has been obtained. These data indicate that the altered pyroclasic sediments of the Kuroko area as a whole comprise two zones, a montmorillonite-zeolite zone and an underlying sericite*-chlorite zone, and that the Kuroko deposits themselves occur in the sericite-chlorite zone (Otagaki et al., 1969). In their review of Kuroko deposits, Matsukuma and Horikoshi (1970) presented the following zonal arrangement of alteration zones, from the outer to the inner. Zone I : montmorillonite and zeolite zone; outer and intermediate parts of rock piles above the ore body. Zone 11: sericite, chlorite and pyrite zone; inner part of the piles above the ore body. Zone 111: sericite, chlorite and quartz zone; alteration within the orebody. Zone IV: silicified zone; footwall and central parts of the orebody. The relative development of these zones varies from deposit to deposit. Zone I1 is generally extensive in the typical, major deposits, but lacking in relatively small deposits. The alteration zones developed by hydrothermal action occur in the form of halos surrounding the deposits, and are covered by or grade laterally into the regional zeolitic alteration zones of the pyroclastic sediments of the Green Tuff basins. Thus, burial alteration (diagenesis) overlaps to form the alteration patterns around the Kuroko deposits. Such overlapping effects are particularly remarkable in Zone I. 3.2.1.

Zeolitic alteration in Kuroko areas

Studies of the alteration zones over relatively wide areas surrounding the Kuroko deposits in the Hokuroku district have been made by Yoshida and Utada (1968) and Iijima (1974), and in the Nishi-Aizu district by Utada et al.

* The name “sericite” is used here as a field or general term denoting fine-grained white micaceous clay, which may consist mainly of dioctahedral mica and/or interstratified minerals of dioctahedral mica with some montmorillonite, although in most recent articles on the clay minerals of Japan, sericite is used as a mineral name for fine-grained dioctahedral mica of hydrothermal origin.

ALTERATION PATTERNS

131

(1974). These studies referred especially to the zonal patterns of zeolitic alterations apart from the Kuroko deposits. The zeolites identified in montmorillonite-bearing rocks in these Kuroko areas include mordenite, clinoptilolite, analcime and laumontite. The sequences of the various zeolite zones differ somewhat from those found in usual burial alterations. In particular, the distribution of analcime is unique, suggesting a close relation with the Kuroko deposits. Iijima (1974) noted that the analcime zone intervenes in the clinoptilolitemordenite zone, and considered that the analcime zone was formed by a reaction between clinoptilolite-mordenite tuff produced by diagenesis and a hydrothermal solution rich in Na derived from the alteration zones proximal to the Kuroko deposits. Utada et al. (1974) have emphasized that the analcime zone can be used as an indicator for exploration of the Kuroko deposits.

3.2.2. Alteration of typical Kuroko deposits The alteration in and around the Kuroko deposits themselves generally shows a characteristic zonal pattern. Recently, a detailed study on the mineral distribution has been made by Shirozu et al. (1974) in the alteration zones of the Matsumine deposit of the Hanaoka mine, which is one of the typical, major Kuroko deposits in the Hokuroku district. The alteration zones are divided into the following four zones, similar to those of Matsukuma and Horikoshi (1970) presented above. Zone I: montmorillonite zone (montmorillonite, zeolite, opal). Zone 11: sericite-chlorite zone (sericite, FeMg-chlorite, quartz). Zone IZZ: clay zone (sericite, Mg-chlorite). Zone JV: silicified zone (quartz, sericite). Zones I1 and I11 are subdivided into zones containing feldspars and carbonates (IIA and IIIA) and zones deficient in these minerals but rich in sulfide and sulfate minerals (IIB and IIIB). Fig. 3.3 gives an idealized section of the alteration

Fig. 3.3. Idealized section of the Matsumine deposit, Hanaoka mine, showing the relation of alteration zones (Shirozu et ul., 1974). B-0, Black ore; Y-0, yellow ore; P-0, pyrite ore.

132

WALL ROCK ALTERATION OF KUROKO DEPOSITS

zones, and Table 3.1 shows the mineral associations and their relative abundances. Zone I is characterized by montmorillonite, opal (cristobalite) and mordenite. The textures of the parent pyroclastic rocks in this zone are usually well preserved, and primary plagioclase is unaltered. However, glass fragments of pumice grains and glassy groundmass are altered to aggregates of microcrystalline moiitmorillonite and opal. In the lower part of Zone I, opal is recrystallized to fine-grained quartz aggregates. Near the boundary with Zone 11, interstratified minerals of dioctahedral mica/montmoriIIoniteand of chlorite/saponite occasionally occur in place of montmorillonite. The boundary of Zones I and I1 crosses the stratigraphic boundaries. Zone I1 represents a remarkable alteration zone surrounding the ore deposits, and its thickness exceeds 200 m at maximum in the hanging wall. The main part (IIA) consists largely of an assemblage of sericite, FeMg-chlorite, quartz, albite, K-feldspar and carbonates. The primary plagioclase is replaced by secondary feldspars, sericite, etc., and the groundmass is composed mainly of mosaics of quartz, sericite and FeMg-chlorite. The majority of the sericite is in the form of irregularly interstratified dioctahedral mica/montmorillonite having very small to small amounts of montmorillonite layers, although the montmorillonite component tends to increase near the boundaries with Zone I and Zone IIIA. In Zone IIB the sericite often occurs as non-interstratified dioctahedral mica. Zone I11 is a lenticular clay bed about 1000 X 1000 X 100 m in size enclosing the main ore deposits which comprise several stratiform ore bodies. In this zone, the original textures of the parent rocks are barely distinguishable, and the clays, comprising many clay minerals as shown in Table 3.1, are often moriomineralic. The sericite, which is most abundant in Zone 111, is characterized by interstratifications of dioctahedral mica and montmorillonite, particularly by the 1:1 regular interstratification found in the hanging wall clay. Mg-chlorite is second most widespread. Gypsum and pyrite are common in the main part of this zone (IIIB). Quartz is not common in Zone 111. Zone IV consists of silicified rhyolite and pyroclastic rocks with some accompanying stockwork ores. It is characterized by associations of quartz and sericite, the latter consisting of relatively well-crystallized dioctahedral mica. The distribution of clay minerals in Zones TI1 and IV is closely related to the zoning of ores shown in Fig. 3.2, which is based on data for several Kuroko deposits in the Hokuroku district as well as the Matsumine deposit (Shirozu, 1974). At the lower central part of the ore deposits, well-crystallized dioctahedral mica occurs in the silicified felsic lava dome or breccia. The upper part of the silicified zone grades into siliceous stockwork ore, in which well-crystallized mica is also found. Lateral to the silicified zone there are often gypsum ores accompanied by Mg-chlorite and some sericite. The mineralogical character of the sericite changes laterally from mica to interstratified mica/montmorillonite with increasing distance from the silicified zone. Most of the clays of the upper hori-

TABLE 3.1. Mineral associations in a!teration zones of the Matsumine deposit, Hanaoka mine (Shirozu et al., 1974) 1

I1 Sericite-chlorite zone IIA IIB

Montmorillonite zone Uuuer Lower Opal Quartz Mordenite K-feldspar Plagioclase (albite) Montmorillonite Dioct. mica/montmorilIonitetl Dioct. mica/(montmoriIlonite)t2 Dioctahedral mica Chlorite/saponite Chlorite Sudoite Dioct. mica/sudoite Kaolin Pyrophyll ite Calcite Dolomite Gypsum and anhydrite Pyrite

++++ + + + -F+++++

+

+++ ++++ ++ ++ +++++ + + + +

++++ +++ +++ + + +++ 4-4+ +++

+

++

++

+ Upper or outer

Ill Clay zone IIIA IIIB

+++ ++ ++ ++++ +++ +++ +++ ++ +++ ++ + -I-+ + +++ +

-

++

IV Silicified zone

+++++

++ ++++ + ++ ++++ ++ ++++ + + + ++ + ++++ + +++ ++

Lower or inner

t lDioct. mica/montmorillonite: interstratified dioctahedral mica/montmorillonite with abundant montmorillonite layers, showing long spacing reflections. tzDioct. mica/(montmorillonite): interstratified dioctahedral mica/montmorillonite having small amounts of montmorillonite layers. L

W W

134

WALL ROCK ALTERATION OF KUROKO DEPOSITS

zons, in which stratiform metallic ores develop, are composed of interstratified mica/montmorillonite with considerable amounts of montmorillonite layers, occasionally accompanied by Mg-chlorite. Within the metallic ores, interstratified minerals are rare. Chlorite is often found in yellow and pyrite ores, but is rare in black ore. In the metallic ores, the clay minerals are often crystallized in close paragenetic relation with non-clay minerals at the microscopic level. The hanging wall clay consists mainly of interstratified mica/montmorillonite with the largest amount of montmorillonite layers in Zone 111, although the amount is small above the central part of the deposits. Interstratified Mg-chlorite/ saponite occurs in the hanging wall in association with interstratified mica/montmorillonite. Where ferruginous chert is present, it is usually associated with FeMg-chlorite. Thus the clays occurring in the ore zones are composed mainly of sericite and chlorite minerals. Kaolin minerals and pyrophyllite are found locally in the upper horizons, usually in association with black ore. Sudoite, tosudite (1 :1 regularly interstratified sudoite/montmorillonite) and I :I regularly interstratified dioctahedral mica/sudoite are found rarely in the hanging wall and footwall clays. Shirozu et al. (1974) have suggested that these complicated stratigraphic and concentric zonal alteration patterns exhibit both syngenetic and epigenetic alteration, and that the clay bed of Zone I11 was formed syngenetically by a reaction between hydrothermal ore solutions and volcanic glasses on the sea floor. The concentric zonal patterns, including the A-B zonation in Zones I1 and 111, may have resulted from hydrothermal activity with a center at the silicified rhyolite dome, which continued during and after deposition of the ore and hanging wall sediments. Iijima (1974) has estimated that the hydrothermal activity continued for about 1 to 2 million yr after the ore deposition in the Hokuroku district. The chemical changes in the rocks associated with these alterations have been discussed by Iijima (1974), Utada et al. (1974) and Lambert and Sat0 (1974). The most significant changes are : enrichment of Si in Zone IV, of Mg in Zones I, I1 and 111, and of K in Zones 11, 111 and IV; and depletion of Na in Zones IT, I11 and IV.

3.2.3. Alterations in some other Kuroko deposits There are various modes of alteration of Kuroko deposits which differ somewhat in zonal pattern and mineral associations from those described above. Some of these will be noted briefly below. As mentioned, the sericite-chloritezone is lacking in the hanging wall of some relatively small deposits. In these deposits the montmorillonite zone directly overlies the clay zone, which is comprised mainly of sericite and chlorite and encloses the stratiform ores. In many such deposits, interstratified minerals of dioctahedral mica/montmorilbnite and of chlorite/smectite occur in a transi-

ALTERATION PATTERNS

135

tional zone between the clay and montmorillonite zones (Hayashi, 1961;Igarashi, 1969; Igarashi and Sawada, 1971; Yamaoka and Asakura, 1974; etc). In some deposits, distinct hanging wall clays consisting mainly of montmorillonite can be recognized. Saponite is also rarely found. In the case of the Yoshino mine, the hanging wall clay, which is called “Matsukawa (lit. pine-tree bark) clay” and colored various shades of brown, is known to consist of montmorillonite with some kaolin or sericite (Osada et al., 1974). These facts indicate that remarkable hydrothermal activity may not have continued after ore deposition in the case of these deposits, and suggest that the interstratified mica/montmorillonite in the hanging wall clay of the typical, major deposits may have been transformed from montmorillonite. The clays within the deposits are composed principally of sericite and chlorite throughout all Kuroko deposits. The chlorite is usually Mg-chlorite, but other chlorites are occasionally found. Yamaoka and Asakura (1974) have reported the occurrence of FeMg-chlorite, Fe-chlorite and sudoite in some metallic ores of mines in the Nishi-Aizu district. Kimbara and Nagata (1974) have described an alteration product composed of sudoite, tosudite and sericite in a gypsum ore zone from boreholes in the Hokuroku district. In some deposits, the silicified zone in the footwall is very attenuated and replaced by clay alterations composed of sericite and chlorite with frequent associations of gypsum and anhydrite. Kaolin minerals and sudoite are also occasionally found (Iijima, 1974; Yamaoka and Asakura, 1974). On the other hand, silicification is usually associated with the stockwork ore. At the Furutobe mine, relatively large siliceousore bodies underlying stratiform ore bodies display strong silicification accompanying some clay minerals. The variation in clay minerals has been investigated by Kuroda and Odashima (1975) who showed that dioctahedral mica tends to occur in association with the relatively high-grade Cu-ore in the inner part of the silicified zone, and interstratified mica/montmorillonite and chlorite with the low-grade ore in the outer part of the zone. 3.2.4. Alteration of some stockwork deposits

Those metallic ore deposits which are essentially and genetically identical with the common Kuroko deposits but have extremely high proportions of stockwork ore, are called Kuroko-type stockwork deposits. They usually occur in silicified rocks. The alteration patterns around the ore deposits of the Tsuchihata mine, which are composed of several representative stockwork deposits in silicified rhyolite, have been described by Matsukuma (1974). Each unit ore body is generally in the form of a vertically standing pipe of Cu-ore, consisting of intersecting veinlets grading downwards into fissure-filling veins. The ore body is intensely silicified and surrounded by a sericite-chlorite zone and an outer montmorillonite-zeolite zone. This zoning is lateral and upward, and there is also a trend

136

WALL ROCK ALTERATION O F KUROKO DEPOSITS

for silicification, sericitization and chloritization to be remarkable in the upper, intermediate and lower parts, respectively. A unique alteration zone comprising an Al-rich mineral assemblage has been reported in some stockwork deposits by Hayashi (1961). Pyrophyllite, kaolin and diaspore occur as the main alteration minerals around the stockwork deposits (mainly pyrite ore) at the Kamikita (Honko deposit) and Aomori mines. From the Honko deposit of the Kamikita mine, sudoite and tosudite have been reported (Hayashi and Oinuma, 1964; Sudo and Kodama, 1957). 3.2.5. Alteration of some gypsum deposits

As mentioned above, the gypsum ores of common Kuroko deposits tend to be associated with Mg-chlorite. Kuroko-type gypsum deposits, accompanied by only small amounts of metallic ores, are also known to be associated with magnesian chlorite clay (Hayakawa and Takasawa, 1966; Igarashi and Sawada, 1971). The deposit at the Wanibuchi mine may be a representative Kuroko-type gypsum deposit, and the patterns of alteration have been studied by Sudo (1954), Iwao (1956), Katsumoto and Shirozu (1973), Shirozu (1974), etc. Lenticular gypsum ore bodies, which are overlain by small black ore bodies, occur around the boundary or transitional zone between the mudstones (hanging wall) and felsic tuffs (footwall). The wall and gangue rocks are altered to a pale grayish chloritic clay which is surrounded by a montmorillonite zone. The chloritic clay is characterized by assembIages of Mg-chlorite, interstratified Mg-chlorite/saponite and some talc. The latter two minerals occur in close mutual association. Chrysotile serpentine is rarely found. The altered mudstone in the hanging wall consists mainly of interstratified minerals of Mg-chlorite/saponite and of dioctahedral mica/montmorillonite. Well-crystallized sericite consisting of dioctahedral mica is found in a relatively small, silicified rock body which underlies the gypsum ore bodies. 3.3.

CLAY MINERALS

Numerous clay minerals occur in the alteration zones of the Kuroko and Kuroko-type deposits. The reported layer silicates are mica minerals, chlorite minerals, interstratified dioctahedral mica/sudoite, smectites, kaolin minerals, pyrophyllite, serpentine and talc. They are fine-grained, but the crystalline state and properties associated with their hydrothermal origin are intermediate between igneous or metamorphic well-crystallized layer silicates and weathering or sedimentary clay minerals. The characteristics of and variations in their mineralogical properties, particularly regarding the mica minerals, are outlined below together with their main modes of occurrence.

CLAY MINERALS

137

3.3.1. Mica minerals Mica clay minerals, usually called sericite, are the most abundant minerals of the altered wall rocks immediately surrounding Kuroko deposits. They consist of fine-grained dioctahedral K-mica and its interstratifications with montmorillonite. No trioctahedral mica is found as an associated alteration mineral of the deposits. A large number of studies on the clay mineralogy of the sericites has been made (Sudo, 1954; Hayashi, 1961; Shimoda et al., 1969; Shirozu and Higashi, 1972; Shirozu et al., 1972; Shimoda, 1972; Shimoda and Nishiyama, 1973; Higashi, 1974; Higashi and Shirozu, 1975; etc.). The results indicate that the mica clay minerals are composed of three types: (1) dioctahedral mica, (2) interstratified dioctahedral mica/montmorillonite with small amounts of montmorillonite layers, which belongs to the category of irregular interstratification, and (3) interstratified dioctahedral mica/montmorillonite showing long spacing reflections (about 25 A or more), which may belong to the category of 1 :1 regular interstratification. These three types of minerals apparently form an almost continuous series. As described in section 3.2, the first type, non-interstratified mica, occurs mainly in the silicified zone and siliceous ores as white sericite which forms networks or aggregates with quartz, pyrite, etc. in a relatively well-crystallized state, although no macroscopic flakes have been found. It occurs also in parts of the clay zone enclosing the stratiform ore bodies and in the sericite-chlorite zone. The second type, which has small but variable amounts of montmorillonite layers (ca. 5-25 %), occurs most extensively. It forms white to pale gray clays with a silky luster in the clay zone, and is often found as monomineralic clay. In the sericite-chlorite zone it occurs as a constituent of green-colored altered rocks with FeMg-chlorite, quartz, feldspars, etc. The third type, 1 :1 regularly interstratified mineral, is found mainly in the hanging wall and around the ends of lenses in the clay zone, usually as pale gray clay. It has also been reported from transitional zones between the montmorillonite and sericite-chlorite or ciay zones. The non-interstratified mica gives relatively sharp basal X-ray reflections of 10.0 A integral series, which agree with those of usual dioctahedral K-mica. Compared to this pattern, the irregularly interstratified mica/montmorillonites having small amounts of montmorillonite layers give the first 10 A reflection at a slightly larger d-spacing (10.1-11.0 A) and the third, 3.3 A one at a slightly smaller d-spacing (3.30-3.33 A), both of the line profiles being relatively broad, but the second, 5 A reflection is almost fixed and relatively sharp. These characters together with the changes of pattern on solvation agree well with those of common irregularly interstratified mica/montmorillonites such as illite in sedimentary rocks. The proportion of interstratified components can be estimated from the peak migrations on solvation, as is well known. A rough estimation

138

WALL ROCK ALTERATION OF KUROKO DEPOSITS

may also be possible from the d-spacing of the 10 A reflection. Shjrozu and Higashi (1972) have used the relative peak widths of the 10-11 A ( w ~and ) 5A (w2)reflections at half-height to estimate the extent of mixed layering for a large number of sericites from Kuroko deposits. The results indicated a close relation between extent of mixed layering and modes of occurrence as described above. The component proportion in the regularly interstratified minerals showing long spacing reflections may be estimated roughly as 1:l. However, recent studies on three different specimens by Shimoda et al. (1969), Shimoda (1972), and Higashi (1974) estimate the amount of montmorillonite component to be about 40 % for each specimen, mainly by Fourier transforms. The polytypes of sericite identified from powder patterns are usually 2M1, lM, lMd, and mixtures of these. The occurrence of 2M2 polytype has been reported in the Shakanai mine by Shimoda (1970). Unidentified patterns are also occasionally found. It is recognized that 2M1 polytype usually occurs within the ore deposits but 1 M and 1Md are found extensively in the alteration zones (Yamaoka and Asakura, 1974; Shirozu et al., 1974; Higashi and Shirozu, 1975). In regard to mixed layering, the patterns of 1Md are recognized in interstratified minerals having considerable amounts of montmorillonite layers, so that Shirozu et al. (1972) and Shirozu (1974) have ascribed the 1Md pattern in the Kuroko sericites to interlayering of montmorillonite layers. However, Shimoda and Nishiyama (1973) have encountered cases which are difficult to explain with this idea. Chemical analysis of the sericites shows a restricted range of chemical variation: rich in A1 and poor in Mg and Fe. Some of the analyses are given in Table 3.2. The numbers of cations in the table were obtained on the basis of Olo(OH)2 except those for No. 2, which are based on 12(0,0H). As a whole, they show an intermediate composition between usual muscovite and sedimentary illite; the numbers obtained for tetrahedral A1 are a little less than 1.0, and those for interlayer cations are also less than 1.0 even in the non-interstratified mica. The numbers of interlayer cations, mainly K, and the contents of water, particularly H20 (-), vary with the proportions of interstratified components. The total numbers of octahedral cations are 2.02-2.10. The Fe and Mg amounts differ subtly from specimen to specimen, and some analyses (e.g. No. 4 in Table 3.2) are close to those of phengite. Higashi (1974) and Higashi and Shirozu (1975) have suggested that the amounts of these octahedral minor components, which are reflected in the d(060) value and also in the IR band frequency at about 530 cm-l, relate closely to the polytypes and the DTA curves (see below). Shirozu et al. (1974) have examined the variations in extent of mixed layering and octahedral composition of sericites in alteration zones of the Matsumine deposit of the Hanaoka mine. They used the 10 A reflection peak width (w1) and the 530 em-1 band frequency to estimate the mixed layering and octahedral compositions, respectively. The results, shown in Fig. 3.4, indicate that there is a definite chemical difference in the mica minerals in addition to the variations in mixed layering already mentioned, i.e. the sericites occurring in close asso-

139

CLAY MINERALS TABLE 3.2. Chemica analyses of mica clay minerals from Kuroko deposits 1) 48.44% 0.14 33.33 1.72 1.46 0.29 0.15 9.80 5.46 0.07

2) 47.14% 0.34 37.09 0.49 0.83 0.57 0.35 7.10 5.18 0.99 P205 0.01 __ 100.86 100.09

sioz Ti02 A1203 Fez03 MgO CaO NazO KzO HzO+ HzO-

~

Total

3) 46.47% 0.50 37.34 0.20 0.46 0.09 0.37 8.85 5.54 0.49 ___

~

5) 46.83% 1.13 33.10 0.97 1.14 0.23 0.89 7.42 6.17 1.59

-

6) 48.88% 0.73 31.35 0.33 0.97 0.54 0.92 5.12 7.58 3.67

99.47

100.09

Tet .

Si A1

3.20 0.80

3.085 0.915

3.08 0.92

3.170 0.830

3.20 0.80

3.37 0.63

1.79 0.09 0.14

1.960 0.020 0.025 0.080

1.99 0.01 0.04

1.781 0.037 0.282

1.87 0.05 0.12

1.91

Oct.

Al Ti Fe3+ Mg

0.02 0.10

Ca Na

0.02 0.01

K

0.83

0.040 0.045 0.595

0.01 0.05 0.75

0.029 0.031 0.674

0.02 0.12 0.65

0.04 0.12 0.45

Interl.

100.31

4) 47.24% 0.25 33.01 0.73 2.82 0.41 0.24 7.87 6.46 1.48 FeO tr 100.51

-

-

+

1) 1M 2M1 dioctahedral mica from the Matsumine deposit, Hanaoka mine, Akita Pref. (Higashi and Shirozu, 1975). 2) 2Mz hydromuscovite from Shakanai mine, Akita Pref. (Shimoda, 1970). 3) 2M1 interstratified mica/montmorillonite (5 % mont. 1.) from Shakanai mine, Akita Pref. (Higashi, 1974). 4) 1M interstratified mica/montmorillonite (20% mont. I.) from a Kuroko deposit at Niida, Odate, Akita Pref. (Kimbara and Nagata, 1974). 5) 1 M 2M1 interstratified mica/montmorillonite (15-25 % mont. I.) from the Uwamuki deposit, Kosaka mine, Akita Pref. (Higashi, 1974). 6) 1Md 1 :1 interstratified mica/montmoriIlonite (40% mont. I.) from the Matsumine deposit, Hanaoka mine, Akita Pref. (Higashi, 1974).

+

ciation with the ores have lower Mg and Fe contents than the sericites in the surrounding alteration zones. It may be of interest and significant that this pattern of variation in the mineralogical properties of sericites bears a similarity to the idealized arrangement of alteration zones shown in Fig. 3.3. The polytypes are identified mostly as 1Md in the case of the plots in the upper half of Fig. 3.4, as 1M on the lower left-side, as 2M1 on the lower right-side, and as mixtures of 1M and 2M1 in the lower intermediate area. Some specimens on the lower right-side (with the least Mg and Fe contents) show 2M2 or unidentified polytype patterns (Higashi and Shirozu, 1975). DTA curves of the mica minerals from Kuroko deposits have been examined in detail by Shimoda et al. (1969), together with those of many dioctahedral mica clay minerals of different origins. They indicated that there are two types of minerals, with a single endothermic peak and with double ones due to dehydroxyl-

WALL ROCK ALTERATION OF KUROKO DEPOSITS

140

0

:. I.OL

0

0

3 535

520

525

530

Wave number (crn-')

( 6 ) lv

0 B-0

Y Y-0

P P-0

4

Fig. 3.4. Variation in the 10 A reflection width (WI) and 530 cm-l IR band frequency of sericites (dioctahedral mica and interstratified dioctahedral mica/montmorillonite) from alteration zones of the Matsumine deposit, Hanaoka mine (Shirozu er al., 1974). The montmorillonite component increases upwards, and the Mg and Fe contents decrease rightwards. The plots are classified according to the alteration zones and ores shown in Fig. 3.3, from which the samples were obtained.

ation between 500 and 750°C, and concluded that the minerals with a single peak are undergoing transformation of mica to montmorillonite and those with double peaks are undergoing the reverse process, as suggested by Cole and Hosking (1957). However, Higashi (1974) and Higashi and Shirozu (1975) have ascribed the single and double peaks to the very small and small Mg (and Fe) contents, respectively. It is known that the specimens No. 2 and 3 in Table 3.2 give a single peak, whereas the others give double peaks.

3.3.2.

Chlorite minerals

Chlorite minerals are the next most widespread after mica minerals in the alteration zones of Kuroko deposits. Numerous studies have revealed that

CLAY MINERALS

141

their chemical compositions vary considerably. Shirozu (1 974) subdivided them into five types : (I) Mg-chlorite, (2) interstratified Mg-chlorite/saponite, (3) FeMg-chlorite, (4) sudoite. and ( 5 ) 1 :1 regularly interstratified sudoite/montmorillonite (tosudite). The former three minerals are trioctahedral, and the latter two are dioctahedral. Most of them, except FeMg-chlorite, occur as grayish white clay with or without a greenish tint in the clay zone. They are often monomineralic, and have been studied in detail (see Chapters 7 and 8). The following paragraphs summarize the modes of occurrence and characteristics of these chlorite minerals. Mg-chlorite is common in Kuroko deposits. It occurs in the clay zone together with sericite, and is often associated with various ores, particularly gypsum ore, but is rare in black ore. Pyrite is usually associated with it, but association of quartz is rare. The Mg-chlorite is rich in Mg, generally poor in Fe, and considerably variable in Al. Most of the Mg-chlorites are considered to be leptochlorite, which belongs to the trioctahedral series but is deficient in octahedral cations by substitution of 2A1 for 3Mg. The b dimensions (9.18-9.215 A) are smaller than those of usual well-crystallized Mg-chlorites (9.21-9.22 A). The polytype is mostly Ilb, but occasionally Ia. The interstratified Mg-chlorite/saponites comprise an irregularly interstratified mineral having a small amount of saponite layers and a 1 :1 regularly interstratified mineral with a long spacing (about 30 A) reflection. These minerals are usually found in the hanging wall clay. In the gypsum deposits of the Wanibuchi mine, they occur abundantly in and around the deposits in close association with talc. The interstratified Mg-chlorite/saponites give a larger relative intensity of the 14 A reflection and larger d-spacings and broader line profiles of basal reflections than those of Mg-chlorite. Chemically, they are relatively rich in Si compared to Mg-chlorite. FeMg-chlorite generally occurs as green dots or patches in altered tuff of the sericite-chlorite zone surrounding the ore deposits. Some may be interstratified minerals with saponite. FeMg-chlorite is also found in association with ferruginous chert in the hanging wall and with some metallic oies (Yamaoka and Asakura, 1974). Sudoite is often found in association, usually with sericite and occasionally with kaolinite, Mg-chlorite, etc. It is not abundant in general, but seems to be distributed widely in the alteration zones. Many chemical analyses of sudoites from Kuroko deposits have shown that they contain large amounts of Al and considerable amounts of Mg. They have a structure with a dioctahedral2:l layer and an interlayer sheet close to trioctahedral but somewhat deficient in cations. The polytype is Ilb. The regularly interstratified sudoite/montmorillonite (tosudite) displays similar modes of occurrence to sudoite. However, when it occurs with sudoite in a deposit, the tosudite tends to occur in the upper horizon (Kimbara and Nagata, 1974). Known tosudites from Kuroko deposits are considered to have a chlorite layer similar to the Kuroko sudoite.

WALL ROCK ALTERATION OF KUROKO DEPOSITS

142

3.3.3.

Regularly interstratified dioctahedral rnicalsudoite

In addition to the above-mentioned interstratified minerals of mica or chIorites with smectites, an unusual interstratification of mica and chlorite is known from the Matsumine deposit of the Hanaoka mine (Shirozu et al., 1971). It is associated with sudoite and sericite in the hanging wall clay. Experimental data indicate that the mineral is essentially a 1:1 regular interstratification of dioctahedral mica and sudoite, containing a small amount of expandable layers. The mineral is considered to be a transformation product of tosudite. 3.3.4.

Srnectites

Montmorillonite (dioctahedral smectite) is a major clay mineral of the montmorillonite and montmorillonite-zeolite zones, which represent the outer alteration zone and are usually at some distance from the ore deposits. However, in some deposits lacking a sericite-chlorite zone in the hanging wall, montmorillonite does occur as a main constituent of the hanging wall clay immediately overlying the ore deposits. Saponite (trioctahedral smectite) is rarely found together with it. Saponite is also reported as a constituent of the montmorillonite-zeolite zone considerably distant from the ore deposits (Iijima, 1974). 3.3.5.

Kaolin minerals

Kaolin minerals occur locally in the clay zone, particularly in the upper, black ore horizon. In the Matsumine deposit of the Hanaoka mine, a clay composed of kaolinite and dickite is intercalated in a black ore body, and small nacrite masses have been found in another black ore body (Shirozu, 1974). In the Kosaka mine, a kaolin-pyrophyllite-diaspore-sericiteassociation is known from black ore (Matsukuma et al., 1974). Many other local occurrences of kaolin minerals have been reported from the alteration zones (Hayashi, 1961; Yamaoka and Asakura, 1974; etc.). In a stockwork deposit of the Aomori mine, nacrite, dickite and kaolinite are known to occur around the pyrophyllite zone which encloses a pyrite ore body (Hayashi, 1961). 3.3.6.

Pyrophyllite

Pyrophyllite shows similar modes of occurrence to the kaolin minerals, and is often associated with them as described above. 3.3.7.

Serpentine

An occurrence of chrysotile serpentine has been reported in the gangue clays of the gypsum deposit of the Wanibuchi mine (Shirozu, 1974). It occurs as small grayish white masses associated with interstratified Mg-chlorite/saponite.

CONCLUSION

3.3.8.

143

Talc

Talc is frequently found in and around the gypsum deposit of the Wanibuchi mine in close association with interstratified Mg-chlorite/saponite. The two minerals form grayish white masses, with or without a greenish tint. 3.4. CONCLUSION

As outlined above, the wall rocks of Kuroko and Kuroko-type deposits show extensive and complicated zonal alteration patterns. There are considerable variations in zonal pattern, mineral associations, etc. from deposit to deposit. However, the main characteristics may be summarized as follows : (1) The alteration of the Kuroko deposits can be characterized according to the following four alteration zones, from the lower or inner to the upper or outer: a silicified zone accompanying stockwork ores, a clay zone enclosing stratiform ore bodies, a sericite-chlorite zone surrounding these two zones, and an outermost montmorillonite zone, (2) The silicified zone is considered to have formed around the center of submarine volcanic activity in the brecciated lava dome, together with siliceous stockwork ores. The associated clay mineral is well-crystallized dioctahedral mica. (3) The clay zone is considered to represent a clay bed formed initially and concurrently with the stratiform ore bodies on the sea floor, although its later burial and hydrothermal realteration are inferred. The clays, which are often monomineralic, consist mainly of sericite (interstratified dioctahedral mica/ montmorillonite), Mg-chlorite and some kaolin. Their distribution is closely related to the zoning of ores. The amount of montmorillonite layers in the interstratified mica/montmorillonite increases upwards to the hanging wall and laterally to the limit of the clay bed. (4) The sericite-chlorite zone develops as a halo surrounding the silicified and clay zones, up to the tuffs and mudstones accumulated above the ore deposits in typical, major deposits. It may have been formed by the hydrothermal activity which continued for some time during and after ore deposition. The zone is characterized by an assemblage of sericite, FeMg-chlorite, quartz and some feldspars. ( 5 ) In some relatively small Kuroko deposits, the sericite-chlorite zone is restricted to the horizons beneath the ore deposits. The hanging wall clay then consists mainly of montmorillonite. (6) The montmorillonite zone is the outermost alteration zone and grades into the adjacent regional zeolitic alteration zone. It is characterized by montmorillonite, opal and zeolites. The sequence of occurrence cf zeolites, particularly the distribution of analcime, suggests that the hydrothermal alterations

I 44

WALL ROCK ALTERATION OF KUROKO DEPOSITS

related to the Kuroko deposits have been superimposed on the diagenetic alterations of this zone. (7) Strong silicification usually accompanies the Kuroko-type stockwork deposits. (8) The alteration of the Kuroko-type gypsum deposits is characterized by the occurrence of magnesian chloritic clay. (9) Numerous clay minerals occur in the alteration zones. The distribution of the alteration minerals and variations in their mineralogical nature, particularly in the case of the mica and chlorite minerals which occur commonly, show a close relationship to the zonal features of the ore deposits and altered wall rocks. REFERENCES Cole, W. F. and Hosking, 3. S. (1957) Differential Thermal Investigationof Clays(ed.R. C. Mackenzie), p. 248-274, Miner. SOC.London. Hayashi, H. (1961) J. Miner. SOC.Japan 5 , 101. Hayashi, H. and Oinuma, K. (1964) Clay Sci. 2, 22. Hayakawa, N. and Takasawa, S. (1966) J. Japan. Assoc. Miner. Petrot. Econ. Geol. 55, 1. Higashi, S. (1974) Clay Sci. 4, 243. Higashi, S. and Shirozu, H. (1975) J . C/ay Sci. SOC.Japan 15, 78. Igarashi, Z. (1969) Mining Geol. 19, 356. Igarashi, 2. and Sawada, T. (1971) J. Mining Metall. Inst. Japan 87, 389. Iijima, A. (1974) Geology of Kuroko Deposits (Mining Geol. Spec. Issue 6), p. 267-289, SOC. Mining Geol. Japan. Iwao, S. (1956) Japan. J. Geol. Geograph. 27, 105. Iwao, S., Kishimoto, F. and Takahashi, K. (1954) Geol. Surv. Japan Rept. 162, 1. Katsumoto, N. and Shirozu, H. (1973) Sci. Rept. Dept. Geol. Kyushu Univ. 11, 231. Kimbara, K. and Nagata, H. (1974) J. Japan. Assoc. Miner. Petrol. Econ. Geol69,239. Kuroda, H. and Odashima, Y. (1975) Mining Geol. 25, 195. Lambert, I. B. and Sato, T. (1974) Econ. Geol. 69, 1215. Matsukuma, T. (1974) Geology of Kuroko Deposits (Mining Geol. Spec. Issue 6), p. 169-181, SOC. Mining Geol. Japan. Matsukuma, T. and Horikoshi, E. (1970) Volcanism and Ore Genesis (ed. T. Tatsumi), p. 153-179, Univ. Tokyo Press. Matsukuma, T., Niitsuma, H., Yui, S. and Wada, F. (1974) Geology of Kuroko Deposits (Mining Geol. Spec. Issue 6), p. 349-361, SOC.Mining Geol. Japan. Osada, T., Abe, M. and Daimaru, K. (1974) Geology of Kuroko Deposits (Mining Geol. Spec. Issue 6), p. 183-187, SOC. Mining Geol Japan. Otagaki, T., Tsukada, Y., Osada, T. and Fujioka, H. (1969) Mining Geol. 19, 285. Sato, T. (1974) Geology of Kuroko Deposits (Mining Geol. Spec. Issue 6), p. 1-9, SOC. Mining Geol. Japan. Shimoda, S. (1970) Clays Clay Miner. 18, 269. Shimoda, S. (1972) Clay Sci.4, 115. Shimoda, S. and Nishiyama, T. (1973) J. Clay Sci. SOC.Japan 13, 48. Shimoda, S., Sudo, T. and Oinuma, K. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 197. Shirozu, H. (1974) Geology of Kuroko Deposits (Mining Geol. Spec. Issue 6) p. 303-310, SOC.Mining Geol. Japan. Shirozu, H. and Higashi, S. (1972) Clay Sci. 4, 137. Shirozu, H., Ozaki, M. and Higashi, S. (1971) Clay Sci. 4,45.

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Shirozu, H., Date, T. and Higashi, S. (1972) Mining Geol. 22,239. Shirozu, H., Hashiguchi, H. and Honda, S. (1974) Mining Geol. 24,415. Sudo, T. (1954) Sci. Rept. Tokyo Kyoiku Daigaku Sec. C , 3, 173. Sudo, T. and Kodama, H. (1957) Z . Kuist. 109, 379. Tatsumi, T. and Watanabe, T. (1971) Proc. IMA-IAGOD Meetings 1970. IAGOD Vol. (Mining Geol. Spec. Issue 3), p. 216-220, SOC.Mining Geol. Japan. Tokunaga, M. and Honma, H. (1974) Geology of Kuroko Deposits (Mining Geol. Spec. Issue 6), p. 385-388, SOC.Mining Geol. Japan. Utada, M., Minato, H., Ishikawa, T. and Yoshizaki, Y. (1974) Geology of Kuroko Deposits (Mining Geol. Spec. Issue 6), p. 291-302, SOC.Mining Geol. Japan. Yamaoka, K. and Asakura, E. (1974) Geology of Kuroko Deposits (Mining Geol Spec. Issue 6), p. 363-370, SOC.Mining Geol. Japan. Yoshida, K. and Utada, M. (1968) Mining Geol. 16, 333.

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Chapter 4 Allophane and imogolite

Koji WADA

Allophane is considered collectively to constitute noncrystalline hydrous aluminosilicates, and imogolite is a unique paracrystalline aluminosilicate. These minerals form two of the most common clay constituents of soils derived from volcanic ash over a wide range of climatic conditions. Allophane and imogolite strongly influence the physical and chemical properties of such soils, are often responsible for their low productivity, and affect the suitability and quality of the soils as building materials. It has been estimated that ejecta from volcanoes cover up to about 20 X,of the total land surface area of Japan and about 60% of the upland soil is derived from such volcanic materials (Kawaguchi, 1975). Volcanic ash also occupies large tracts of western South America, Central America, the Pacific Northwest of the United States, the Philippines, Indonesia and New Zealand, and some parts of the Antilles and Africa with current or recent volcanic activity. The presence of allophane in soils derived from parent material other than volcanic ash and pumice has also been suggested by various investigators. As reviewed by Wada and Harward (1974), however, the evidence is largely inconclusive and further work is needed. Despite the many investigations, our knowledge of allophane and imogolite is still limited and satisfactory concepts for these minerals are only just beginning to develop. The present Chapter thus reviews the available literature on the mineralogical and chemical properties of allophane and imogolite. Only brief mention is made of allophanes formed in deposits and rivers by hydrothermal alteration, precipitation or other mechanisms, due to the scarcity of data. It is hoped therefore that certain broad generalizations will emerge from this review, and that further research on the nature and properties of allophane and imogolite, and on the utilization of soils and materials containing them, will be stimulated. 4.1.

CHEMICAL COMPOSITION

Seki (1926) published a summary of results for the chemical analysis of 48 soils derived from volcanic ashes in Japan. He analyzed that part of the soils which was dissolved by hot 20 HCI and found that the molar ratios of SiOz, 147

148

ALLOPHANE AND IMOGOLITE

FezO3, “base” and CaO to A1203 were 1.00-2.04, 0.14-0.33, 0.09-0.29 and 0.92-0.09, respectively. “A remarkable deficiency in silica and bases, especially in the latter” was pointed out as a feature common to these soils. Later, chemical analysis after fusion was carried out on non- to poorlycrystalline clays (<2 pm) separated from ash-derived soils and weathered pumices by several investigators, e.g. Birrell and Fieldes (1952), Nozawa (1953), Aomine and Yoshinaga (1955), Kuwano and Matsui (1957), and Iimura (1969). The results indicated that more than 95 % of each clay consisted of Si02, A1203, Fez03 and H20(+), and that the molar Si02/A1203ratios ranged from 0.89 to 2.42. The SiO2/AI203ratios reported for geological allophanes of various origins range from 0.44 to 1.86 (Ross and Kerr, 1934; White, 1953; Ossaka, 1960). Chukhrov et al. (1964) have given Si02/A1203ratios ranging from 1.06 to 2.00 for vitreous allophanes from various deposits in the U.S.S.R. Brown (1955) proposed a scheme for the classification of noncrystalline clay minerals on the basis of their chemical composition. This scheme included opaline silica (SOz.nH20), limonite (Fe203.nH20), kliachite (A1203.nH20), allophane (A1& - 2SiO2.nH20),and hisingerite (2Si02*Alz03.nH20) as end members as well as intermediates between them. With advances in the characterization and purification of clay mineral constituents, chemical analytical data for allophane and imogolite were provided by Yoshinaga and Aomine (1962a,b), Yoshinaga (1966, 1968) and Miyauchi and Aomine (1966b). For these analyses, the (0.2 pm fraction was collected and pretreated with dithionite-citrate to remove “free iron oxides” (Mehra and Jackson, 1960) and with 2 % Na2C03 solution to remove “free alumina and silica” (Jackson, 1956). Based on these data, Wada and Yoshinaga (1969) showed that the SiOz/A1203ratio of clay in which allophane predominates is in the range of 1.3 to 2.0, while that of clay in which imogolite predominates is in the fairly narrow range of 1.05 to 1.15. The H20(+)/A1203 ratio is mostly in the range of 2.5 to 3.5, with no significant difference between the two groups of clays. Higher Si02/A1203ratios for imogolite, i.e. 1.5 (Russell et al., 1969) and 1.29 to 1.32 without chemical pretreatment (Tazaki, 1971), as well as lower values close to 1.0 for allophane (Russell et al., 1969; Lai and Swindale, 1969), have also been reported. More recently, Henmi and Wada (1976) determined the SiOz/Al2O3iatios of 16 clays of different origin ((0.2 pm; without any of the pretreatments described above), for which the relative content of allophane and imogolite was estimated by electron microscopy. As shown in Fig. 4.1, the results indicated that imogolite has a SiOz/Al203ratio close to 1.O, whereas allophane has a Si02/A1203ratio ranging at least from 1 to 2. The limits of the Si02/A1203ratio of allophane have not yet been well defined. Dissolution analysis and difference infrared spectroscopy of many volcanic ash-derived soil clays have shown that dithionite-citrate soluble fractions with a SiOz/Al2O3ratio exceeding 0.2 showed spectral features of allophane (Tokashiki and Wada, 1972, 1975), whereas those with the ratio below 0.2 did not (Wada

CHEMICAL COMPOSITION

149

Fig. 4.1. Relationship between SiOz/AlzOa ratio and content of allophane in fine clays (<0.2 pm) separated from weathered ash and pumice samples (Henmi and Wada, 1976; reproduced by kind permission of the Mineralogical Society of America).

and Wada, 1976) (CJ: Figs. 4.8a, 4.9, below). The mineral constituents in the former fractions were accordingly named allophane-like constituents, whereas those in the latter fractions were considered as alumina-rich gel-like materials or noncrystalline hydrous alumina (Wada and Greenland, 1970). Some possibility remains that allophane-like constituents coexist with hydrous alumina, and therefore the lower limit of the SiOz/AI2O3ratio for allophane was indeterminate. Allophane-like constituents were also present in the 2 % N a ~ C 0 3soluble fraction. Their SiO2/AlZO3ratio was different from that of the constituents in dithionite-citrate soluble fractions, the former values ranging from 0.40 to 1.40 and the latter from 0.19 to 0.81 (Tokashiki and Wada, 1972, 1975). The allophane and imogolite remaining after such dissolution treatment were dissolved by treatment with 0.5 N NaOH and had an SiOz/A1203ratio in the range of 1.04 to 2.49 (Tokashiki and Wada, 1972, 1975). Allophane-like constituents were usually present in association with the allophane and imogolite (Wada and Greenland, 1970; Wada and Tokashiki, 1972), but they alone were present in association with humus in relatively young ash-derived soils (Tokashiki and Wada, 1975; Mizota and Aomine, 1975a,b). 'The question whether "free" alumina is present in ash-derived soils has been discussed. Seki (1926) stated that alumina which was practically free from silica could be extracted by boiling such soil in 10% NaZCO3 solution. Dissolution analysis and difference infrared spectroscopy have revealed that noncrystalline hydrous alumina is present, probably in association with humus, in certain ashderived soils of the temperate regions (Wada and Greenland, 1970; Mizota and

ALLOPHANE AND IMOGOLITE

150

Aomine, 1975a,b; Tokashiki and Wada, 1975). Large amounts of noncrystalline hydrous alumina and iron oxides were also found in Hawaiian volcanic ash which had been weathered under perhumid climatic conditions (Wada and Wada, 1976). Laminar circular or ellipsoidal particles termed opaline silica by Shoji and Masui (1969a,b; 1971) were found at greatest abundance in the 0.4-2 pm fractions of young ash-derived soils. They were soluble in hot 0.5 N NaOH, and the SiOz/A1203ratios of the soluble fraction of those soil clays which contained many opaline silica particles were in the range of 2.4 to 21.7. Fig. 4,2a, b shows electron micrographs of an isolated ellipsoidal particle and of weathered volcanic glass fragments, together with the energy spectra of the X-rays emitted from

I Si

LiC'L,,

LFe

Al

Fig. 4.2. Electron micrographs and X-ray emission spectra. [a) Opaline silica; Yoshibu (3181; Tokashiki and Wada, 1974), 0.2-2 pm. (b) Volcanic glass; Choyo (PA; Henmi and Wada, 1976), 0.2-2 pm. (By courtesy of H. Yotsumoto and S. Aida of the Japan Electron Optics Laboratory Company, Ltd.) Scale-lines: 1 pm.

OPTICAL PROPERTIES

151

them. It is evident that the ellipsoidal particle contains silicon but not aluminum, whereas the volcanic glass fragments contain both silicon and aluminum. A higher SiOz/A1203ratio for 0.5 N NaOH soluble fractions of soil clays containing allophane and imogolite but not opaline silica has been obtained, i.e. 2.45 (Tokashiki and Wada, 1972, 1975; Mizota and Aomine, 1975a,c). The above observations suggest that there is no continuous transition between allophane and opaline silica, and that the highest Si02/Alz03 ratio of allophane is probably less than 3. Yoshinaga (1966) reported that a small but significant amount of Fe (0.30.9 % Fe203) remained in allophane even after 10 successive dithionite-citrate treatments. Sudo and Nakamura (1952) and Kohyama and Sudo (1975) found hisingerites in a pyrrhotite deposit and in clayey volcanic rock fragments in a tuff: the SiOz/Fez03ratios were 3.83 and 2.14, respectively. These hisingerites were identified as very poorly crystalline nontronite. However, the hisingerite defined by Brown (1955), i.e. as an iron analog of allophane, has never been found in weathered volcanic ash. Gotz and Masson (1971) developed a chemical procedure for differentiating silicate anions possessing low degrees of polymerization. The procedure was based on conversion of the anion to a trimethylsilyl ether, and subsequent identification and quantitative determination of the volatile ether by gas chromatography. Application of this technique to imogolite and allophane gave a high yield of the orthosilicate ether. The relative yields of SO4, Siz07,Si3OlOand Si4012ether were 95, 5 , O and 0, respectively, for imogolite and 120, 17,4 and 2, respectively, for allophane with a SiO2/A1203ratio of 0.73 (Cradwick et al., 1972). This provided evidence in favor of the presence of isolated orthosilicate groups in imogolite. Allophane and imogolite as well as other noncrystalline clay materials have a large specific surface area and high chemical reactivity. These materials are more sensitive to chemical dissolution than crystalline clay minerals, and dissolve in accordance with their chemical composition. Many investigators have therefore studied the chemical dissolution processes in order to determine noncrystalline clay constituents. Table 4.1 gives a summary of the principal reagents and dissolution characteristics. 4.2. OPTICAL PROPERTIES

Few determinations of the optical properties of allophane have been reported. Aomine (1958) and Grim (1968) gave index values of 1.49-1.51 and 1.468-1.512, respectively, for allophanes of varied origins. Shioiri (1934) reported an index value of 1.48-1.49 for a dried sample of gel films in a weathered pumice bed. The material did not exhibit double refraction and was identified as allophsne on the basis of its Si02/A1203ratio of 1.0 to 1.1

152

ALLOPHANE A N D IMOGOLITE

TABLE 4.1. Dissolution of Al, Fe, and Si in various clay constituents and humus complexes by treatment with different reagents (modified from Wada, 1977) Element in: Specified component and complex

Treatment with: 0.1 M Dithionite Na4PzOP -citratez)

2% 0.15-0.2 M N ~ Z C O ~ ~ oxalate) oxalic acid (pH 3.0-3.5)4)

0.5 N NaOH5)

A1 in: good good good good Organic complexes good Hydrous oxides Noncrystalline good poor good good good Crystalline none none poor poor good Fe in: none good Organic complexes good good none Hydrous oxides none Noncrystalline good good none poor Crystalline none none none good none Si in: none Opaline silica none none poor good none Crystalline silica none none none poor Al and Si in: Allophane-like good good good good poor Allophane good poor good poor poor good-fair Imogolite good poor poor poor poor-fair none none Layer silicates none none 1) McKeague et n G 9 7 1 ) ; Wada andHigashi (1976). 2) Mehra and Jackson (1960); Wada and Greenland (1970); Tokashiki and Wada (1975). 3) Jackson (1956); Wada and Greenland (1970); Tokashiki and Wada (1975). 4) Schwertmann (1964); Higashi and Ikeda (1973); Fey and LeRoux (1975); Wada and Wada (1976). 5 ) Hashimoto and Jackson (1960); Wada and Greenland (1970); Fey and LeRoux (1975); Tokashiki and Wada (1975).

and staining test results with methylene blue (no blue color) and acid fuchsine (red). Later, Shioiri (1952) noted that these gel films had an anomalous double refraction, and their main constituent was subsequently identified as imogolite by X-ray analysis and electron microscopy(Miyauc1ii and Aomine, 1966b). This anomalous double refraction will be discussed in the next section on the basis of electron microscopy of the films. 4.3. ELECTRON MICROSCOPY

Electron micrographs of allophanic clays derived from weathered volcanic ash and pumice have suggested that allophane consists of aggregates of very fine particles (e.g. Birrell and Fieldes, 1952; Aomine and Yoshinaga, 1955; Egawa and Watanabe, 1964; Bates, 1971). Birrell and Fieldes (1952) reported that the smallest particles of allophane showed no external regularity and were 50 A or

ELECTRON MICROSCOPY

153

less in equivalent diameter. Sudo (quoted by Bates, 1971) found rounded grains or particles (0.1-0.3 pm) usually composed of fine allophane particles (about 500 A in diameter) in volcanic ash-derived soils. Electron micrographs of samples labeled as “mineral)’ or “precipitate” allophane showed particles and aggregates of irregular but rounded outline (Egawa and Watanabe, 1964; Bates, 1971). On the other hand, Aomine and Yoshinaga (1955) noted that very fine hairlike particles predominated in certain ash-derived soils. Subsequently, Yoshinaga and Aomine (1962a,b) distinguished two clay mineral constituents in these soils; one was amorphous to X-rays and named allophane, while the other showced some degree of order and was termed imogolite after the local name of the soil, "Imago". They concentrated allophane in the fraction dispersed in alkali, and imogolite in the fraction dispersed only in acid. Under the electron microscope, imogolite appeared as thread-like particles several pm in length and 100200 A in width, whereas allophane appeared both as “fibrous” and globular particles. Use of the thread-like morphology as the easiest method for identifying imogolite was suggested, but some ambiguity remained over its distinction from “fibrous” alIophane or a possible intermediate between allophane and imogolite. Aomine and Miyauchi (1965) therefore distinguished imogolite A and B which were alike in morphology but different in degree of structural organization, as indicated by the absence or presence of an endothermic peak at 420°C on DTA curves. Kanno et al. (1968) also interpreted their findings as indicating a phase intermediate between allophane and imogolite rather than incomplete separation of the phases. However, Russell et al. (1969) identified the problem as simply one of efficiency of separation. It was considered unrealistic to suggest the existence in the same environment of two different phases possessing a similar, unique morphology. Improvements in instrumentation and techniques of preparation for electron microscopy in the late 1960’s marked the beginning of a new era in the study of imogolite and allophane. Yoshinaga et al. (1968) first obtained high resolution electron micrographs which showed that imogolite threads with a diameter of 100-200 A actually consisted of a finer filiform unit with separations of the order of 18-20 A. Further studies on samples dispersed on a microgrid (Wada et a?., 1970) revealed that these filiform units were bent but ran almost parallel, and were never single but always occurred in pairs. They suggested that imogolite consists of bundles of tube units and that the observed pair of filiform units represents the tube wall. The outside diameter of the tube unit was estimated as 17-21 A, and the inner diameter as 7-10 A. A number of rings with similar diameters were also observed on electron micrographs when the imogolite threads were embedded in methacrylate resin and sectioned normal to their axis with an ultramicrotome. Fig. 4.3 illustrates these features in two purified samples of imogolite. A clear-cut difference in finer morphology between allophane and imogolite

154

ALLOPHANE AND IMOGOLITE

Fig. 4.3. Electron micrographs of purified samples. (a) lmogolite (Maui; gel film); dispersed threads. This sample was studied by Wada et al. (1972). Obtained by N. Yoshinaga. (b) Imogolite (Kurayoshi; gel film); thin section. This sample was studied by Wada et al. (1970). Obtained by H. yotsumoto, K. Ibe and S . Aida. Scale-lines: 500 A.

was pointed out by Wada and Yoshinaga (1969), although the fine structure of allophane was not elucidated. Kitagawa (1971) obtained high resolution electron micrographs of clays separated from five samples of weathered pumice and suggested that allophane has a structural unit which is probably a hollow spherical particle of about 55 A in diameter. The presence of similar objects described two-dimensionally as ringlets has also been observed in imogolite and allophane samples (e.g. Wada and Yoshinaga, 1969; Wada et al., 1972), although their identity was not established. Henmi and Wada (1976) separated clays (<0.2 pm) from 16 samples of weathered volcanic ash and pumice of different lithologic compositions, ages and origins, and found that in all the clays, allophane was composed of fine, discrete particles; these were possibly hollow spherules or polyhedrons with diameters of 35-50 A. Fig. 4.4 shows an electron micrograph of such allophane spherules in mutual aggregation and attached to imogolite tubes. Imogolite, though different in amounts, was detected in all the clays, illustrating how useful high resolution electron microscopy can be for detecting imogolite, particularly when it is present in only trace amounts. Since no fibrous particles other than imogolite were found at high resolution, all of those observed at low resolution were designated as imogolite. No particular morphological variation was noted between the allophane spherules present in these clays with SiOz/AIz03 ratios ranging from about 1 to 2 (Fig. 4.1) and those present before and after dithionite-

ELECTRON MICROSCOPY

155

Fig. 4.4. Electron micrograph of allophane spherules and imogolite tubes (Kodonbaru; 905) (Henmi and Wada, 1976; reproduced by kind permission of the Mineralogical Society of America). Obtained by T. Henmi. Scale-line: 500 A.

citrate and 2 % NaZC03 treatment. It was considered that allophane and allophane-like constituents are not “amorphous” but possess a similar, unique morphology as discrete particles. Kanno et al. (1968) obtained electron micrographs of weathered volcanic glass from which many threads spread out. They suggested direct formation of these threads from the volcanic glass, but doubted whether the threads were of imogolite or not. Their reasoning was that ordered imogolite would not be formed earlier than amorphous allophane. Henmi and Wada (1976) observed dense packing of allophane spherules in some weathered glass shards at high resolution. They noted that imogolite tubes were present outside but not inside the glass shards, unless they were broken down into fragments. The interpretation offered was that allophane forms first by hydrolysis of volcanic glass and in sittt precipitation, while imogolite may be formed either by alteration of allophane o r by precipitation from the hydrolyzate outside the glass shards. A similar but megascopic differential formation of allophane and imogolite has been found inside and outside pumice grains, respectively (Wada and Matsubara, 1968; Henmi and Wada, 1976).

156

ALLOPHANE AND IMOGOLITE

The morphology and occurrence of allophane and imogolite has also been studied with the replica technique and scanning electron microscopy. Yoshinaga et al. (1968) observed numerous threads protruding from the surface of gel films in a pumice bed on a carbon replica. Wada and Matsubara (1968) also observed the development of a planar net structure of threads in these films (Fig. 4.5A), and related it to the anomalous double refraction which the gel film shows under a polarizing microscope (cf. section 4.2). They also noted that allophane forms in the crust concentric to the unweathered core of micron-size “subgrains” and their interstices in weathered pumice grains (Fig. 4.5B). Eswaran (1972) observed the fracture surfaces of Japanese volcanic ashderived soils containing abundant imogslite with the scanning electron microscope and found threads or ribbons forming peculiar globules. The presence of much thicker threads (up to 30,000 A in diameter) led him to suggest that the

Fig. 4.5. Electron micrographs obtain by the carbon replica technique. A, Surface of gel film. B, Fresh section of weathered pumice. (Wada and Matsubara, 1968; reproduced by kind permission of the International Society of Soil Science.) Scale-line: 1 ,urn.

X-RAY AND ELECTRON DIFFRACTION

157

pretreatment for transmission electron microscopy may break up these threads of imogolite along planes of weakness. However, scanning electron micrographs of one of these soils obtained by H. Yotsumoto and S. Aida exhibited planar or curved nets or films consisting of twisting threads, as observed in carbon replicas of the gel films, but no thicker threads or globules of the kind observed by Eswaran were found (Wada and Harward, 1974). A difference in the appearance of imogolite in scanning electron micrographs has been reported for gel films subjected to ordinary and critical-point drying procedures (Noishiki and Tazaki, 1975; Tazaki, 1975). Sudo (1953) and Sudo and Takahashi (1955) found many spherules (about 0.1-0.3 pm in diameter) in white clays altered from vitric tuffaceous rocks. Similar spherules were subsequently identified in many weathered volcanic ash and pumice deposits (e.g. Birrell et al., 1955; Kurabayashi and Tsuchiya, 1960; Aomine and Wada, 1962; Nagasawa, 1969). These spherules were composed mainly of halloysite and showed a unique, concentric layer structure. Sudo and Takahashi (1955) suggested the possibility that much smaller allophane particles (200 A) may be included in the spherules and that their rounded shape may be genetically related to the presence of amorphous materials such as allophane. Few attempts have been made to determine whether or not allophane is actually contained in the spherules. Difference infrared spectroscopy, as shown below in Fig. 4.9B, indicated that halloysite but practically no allophane could be dissolved from one such halloysitic clay by hot 0.5 N NaOH treatment (Wada and Tokashiki, 1972). On the other hand, dissolution of allophane as cores and interlayers from another clay by the same treatment method has been suggested by electron microscopy (Askenasy et al., 1973). Sudo (1974) proposed a release of fine particles, assumed to be allophane, from the spherules on one electron micrograph at high resolution, and maintained the name of allophane-halloysite spherules. 4.4. X-RAY AND ELECTRON DIFFRACTION

Ross and Kerr (1934) reported one diffuse X-ray diffraction band and traces of others in the allophane samples they collected. White (1953) found four diffraction bands at 3.5-3.0 A, 2.26-2.08 A, 1.45-1.27 A and 1.22-1.12 A, in allophane samples from an abandoned mine. He interpreted the data as indicating that allophane has a more ordered structure than glass. Similar diffraction bands were later observed in allophanic clays derived from weathered volcanic ash and pumice (e.g. Aomine and Yoshinaga, 1955; Egawa et al,, 1955; Sudo, 1959; Yoshinaga and Aomine, 1962a). In addition to these diffraction bands, one in the range of 11-17 (Minato, 1960) or 11-15 A (Sudo, 1974) has also been ascribed to allophane. Watanabe (1968) studied the small-angle scattering of X-rays by allophane,

158

ALLOPHANE AND IMBGOLITE

halloysite and kaolinite over scattering angles from 8 to 70’ (CUKCU). He found by Jellinek-Solomon-Fankuchen’s method that the largest value of the distribution function M ( R ? occurs at the smallest radius of gyration RY(39 A) in allophane, and in the range larger than 275 A in halloysite and kaolinite. The diameter of the allophane particle as a sphere was calculated to be about 100 A. Okada et al. (1975) carried out X-ray radial distribution (XRD) analysis on allophanes separated from weathered volcanic ashes and pumices, precipitates in rivers, and synthetic aluminosilicates. They estimated the coordination number of aIuminum in these samples from their XRD curves, giving values ranging from 4.7 to 6.0. Peaks on the differential XRD curves were observed at Y = 1.8, 3.0-3.2, and 4.24.5 A in all samples, and the Al(1V)-0 and AI(V1)-0 distances were estimated at 1.70 and 1.95 A, respectively. Okada et al. (1975) further calculated the differential XRD curves of model aluminosilicates consisting of one-, two- and three-dimensional networks of Si-tetrahedra and Al-octahedra, and suggested that the linkages of the tetrahedra and octahedra in allophane probably yielded a two-dimensional order. The X-ray diffraction features of imogolite were first described by Kuwano and Matsui (1957), Kanno (1959) and Kanno et al. (1960). They observed a material present as gel films in weathered pumice beds which showed diffraction bands at about 12 and 8 A. They noted that these bands were not affected by treatment with ethylene glycol and disappeared on heating at 500-600°C, but considered that the material represented an early stage in the formation of layer silicates from noncrystalline material. Yoshinaga and Aomine (1962b) and Miyauchi and Aomine (1966b) later succeeded in concentrating imogolite, showing similar diffraction features in three volcanic ash-derived soil clays and two gel-film samples, respectively. Fig. 4.6 gives X-ray patterns of imogolite in random and “parallel” orientations. Yoshinaga and Aomine (1962’0) also noted that imogolite exhibits a remarkable intensity increase at 17-19 A upon heating at temperatures of 100 to 300°C. The X-ray patterns of imogolite and the change on heating showed no obvious affinities with known clay minerals. They concluded therefore that imogolite is different from both allophane and layer silicates and so constitutes a new mineral, but probably represents as intermediate phase between them. Yoshinaga et al. (1968) first published an electron diffraction pattern of imogolite in addition to high-resolution electron micrographs of the mineral. The electron diffraction from imogolite was subsequently studied by Russell et al. (1969) and by Wada and Yoshinaga (1969). They noted that randomly oriented imogolite threads gave a series of ring reflections, whereas those aligned almost in parallel showed a strong arcing of the reflections (cf. Table 4.2). On the basis of these diffraction patterns and the fiber units observed in the electron micrographs, Russell et al. (1969) identified repeat units in imogolite: 8.4 A parallel to the fiber axis, and 23 A perpendicular to it. Taking the X-ray diffraction into account also, Wada and Yoshinaga (1969) suggested that imogolite forms a

X-RAY AND ELECTRON DIFFRACTION

159

n,

12-20A

X.D. Random

........................

.. ..

................. .. ... . .. . . . . . . . . . . ..:,

Fig. 4.6. X-ray diffraction patterns of imogolite in random and “parallel” orientations. A dotted line shows the X-ray pattern at 300°C on one half the intensity scale. (modified from Wada and Yoshinaga, 1969; reproduced by kind permission of the Mineralogical Society of America).

paracrystal which is an assembly of chain units with a repeat of 8.4 A. In this paracrystal, the chain units were considered to show statistical rotation and continuous shift, and the mean interchain separation was estimated as 17.7 A. Wada and Yoshinaga (1969), on this basis, interpreted the reaction which occurs when imogolite is heated at 100 to 400°C. The progressive change in the X-ray pattern and weight loss suggested rearrangements of the units upon dehydration. This reaction was inhibited in the presence of dithionite-citrate extractable oxides (Wada and Tokashiki, 1972), KCH3CO0, alkylammonium chlorides or humified material (Inoue and Wada, 1968, 1971b; Wada and Henmi, 1972). Table 4.2 lists the electron diffraction data of Cradwick et al. (1972) for imogolite. The indices of the reflections were obtained by assuming an arrangement of cylinders with a repeat unit of 8.4 A along the cylinder axis and an interaxial separation of 23 A. A detailed description of this cylinder unit will be given in section 4.14. Fourier transforms of the structure projected perpendicular to the cylinder axis accounted for the following features of the diffraction pattern: first, the intensities of the OkO rejections fall off sharply after k = 5 ; second, 071 is the strongest of the Olil reflections; third, the 002 and 022 reflections are very weak; fourth, 063 is the strongest of the Ok3 reflections; and fifth, 006 is strong.

160

ALLOPHANE AND IMOGOLITE

TABLE 4.2. Electron-diffraction data for imogolite threads aligned in parallel (Cradwick et al., 1972)

4.5.

d(&

Intensity

Appearance

20-21 11-12 7.8-7.9 5.8-5.7 4.5 4.1 3.7 3.3 3.3-3.1 2.3 2.09 1.40

strong strong strong medium very weak strong medium weak weak weak weak strong

dot dot dot dot dot arc arc arc broad arc broad arc arc arc

kl 10 20 30 40 50 12 32 42 71 63 04 06

THERMAL ANALYSIS

Differential thermal analysis (DTA) has been used to assess the predominance of allophane in a clay. A large endothermic peak between 10O-30O0C, no endothermic peak between 400-7OO0C, and an exothermic peak between 8001000°C on the DTA curve have been listed as basic features of allophane (Birrell and Fieldes, 1952; Sudo, 1954; Fieldes, 1955; Aomine and Yoshinaga, 1955). The thermogravimetric (TG) curves published by Aomine and Yoshinaga (1955) as well as those by Ross and Kerr (1934) indicate a continuous loss of water with increase in temperature. Fig. 4.7(a) shows DTA and TG curves for allophane of established purity. Fieldes (1955) noted differences in DTA curves between two groups of allophanic clays separated from New Zealand volcanic ash-derived soils. The first group lacked the high temperature exothermic peak and showed a small endothermic peak at about 200°C in addition to a larger one below 150°C. The second group had the exothermic peak but lacked the 200°C endothermic peak, He considered that discrete silica and alumina were present in the former clay (allophane B), whereas silica and alumina were combined in the latter clay (allophane A). Several Japanese investigators (Kanno, 1959; Egawa and Sato, 1960; Shinagawa, 1962) have also noted clays separated from young ash-derived soils which showed no high temperature exothermic peak, but none displayed a 200°C endothermic peak. Fieldes (1955) and these investigators considered that weathering of the volcanic ash advanced through allophane B to allophane A. On the other hand, Miyauchi and Aomine (1964) found that (0.2 pm fractions separated from young ash-derived soils gave a strong exothermic peak near 900"C, whereas the 0.2-2 pm fractions showed slight or no evidence of the exothermic reaction. They correlated the absence of the exothermic reaction

THERMAL ANALYSIS (a)

%

%

200

400

600

Temp.

(“GI

800 1000

Fig. 4.7. DTA and TG curves (modified from Wada, 1977). (a) Allophane (<0.2 prn; weathered volcanic ash (VA); Choyo, Kumamoto; SiOz/Alr03 ratio = 1.77; HZOZtreated). (b) Imogolite (<0.2 ,urn; “gel films” in weathered pumice; Kurayoshi, Tottori; SiOz/AIzO3 ratio = 1.02; H20z treated). Heating rate: 20°C per min. Atmosphere: static air. Sample weight: allophane, 15.9 mg; imogolite, 16.6 mg. Analyst: T. Henmi. (Henmi and Wada, Clay Minerals, 10,236; 238,1974; reproduced by kind permission of the Mineralogical Society, London.)

with the predominance of cristobalite, feldspar and quartz, and pointed out that absence of the exothermic peak does not signify the presence of discrete silica and alumina. There are also indications that the presence or absence of the high temperature exothermic peak is related to the Si02/A1203 ratio of the noncrystalline clay. The exothermic reaction was observed for allophanic clays with SiOz/A1203 ratios of 1.32-1.95 (Yoshinaga, 1966) and of 0.89-1.43 (Iimura, 1969). No exothermic peak was found when the Si02/Ala03 ratios of the main constituents of noncrystalline clays separated from ash-derived soils were in the range of 4 to 25 (Uchiyama et al., 1968) or below 0.2 (Wada and Wada, 1976). The main constituent in the former clays was identified as opaline silica (Shoji and Masui, 1969,) and that in the latter was hydrous alumina associated with iron oxides and humus (Wada and Wada, 1976). Ossaka (1962) studied the thermal transformation of natural and artificia€ aluminosilica precipitates which were X-ray amorphous and had various SiOz/ AI203 ratios. He noted that the intensity of the exothermic reaction correlated with the amount of mullite formed upon heating at 1000°C and with the SiOz/Al203 ratio of the precipitates. Wada and Kubo (1973) found that this relationship does not hold for artificial precipitates prepared by different methods,

162

ALLOPHANE AND IMOGOLITE

but the amount of mullite formed correlated with the SiOz/AIz03 ratio of the precipitates. Maximal mullite formation was observed in precipitates with a SiOs/AlZO3ratio of 0.66 (Ossaka, 1962) or of about 1.0 (Wada and Kubo, 1973). The formation of y-alumina (Tsuzuki and Nagasawa, 1960) or Si-A1 spinel (Udagawa et al., 1969) followed by mullite formation from allophane during or immediately after the exothermic reaction, has been indicated by X-ray analysis and electron diffraction analysis. The similarity in such thermal transformation between allophane and kaolinite was regarded as evidence for a sheet structure in allophane. It has been reported in allophanic clays that the products and intensity of the exothermic reaction are affected by exchangeable cations (Miyauchi and Aomine, 1966a) and by previous treatment of the sample preparation (Egawa and Sato, 1960; Miyazawa, 1966). Ossaka (1962) also noted that mullite was formed from natural precipitates with SiOz/A1z03 ratios below 0.2 but not from artificial precipitates, and that y-alumina was formed from natural and artificial precipitates only when their SiO2/AlZ03ratio was below 0.2. The thermal transformation of natural and artificial aluminosilica precipitates was considered important for understanding their structural organization. Kitagawa (1974) has attempted to distinguish adsorbed water and structural hydroxyl groups in two allophane samples by resolving their differential thermogravimetric (DTG) curves into two gamma distributions with maxima at about 90 and 320°C. Omitting the adsorbed water, the hydroxyl groups were estimaled to comprise 13.9 and 14.6 wt% of the allophanes. The molar HzO(+)/Alz03 ratios calculated from the analyses are 1.73 and 1.86. These valrres are considerably lower than the 2.31-2.81 obtained by Yoshinaga (1966) and the 2.652.96 obtained by Iimura (1969) for allophanic clays, and are also lower than the value of 2.00 for kaolinite. Yoshinaga and Aomine (1962b) reported that imogolite showed a DTA curve similar to that of the allophane coexistent with it, but exhibited a small, eminent endothermic peak at 425-435°C due to dehydroxylation. Rapid weight loss was also noted between 275-350°C on the T G curve obtained by plotting the equilibrium weights at each temperature. A similar endothermic peak on DTA curves had been noted for allophanic soil clays (Aomine and Yoshinaga, 1955) and for gel films in weathered pumice beds (Kanno et al., 1960), but was attributed to impurities such as hydrous oxides of iron or aluminum. T G curves obtained for imogolite by continuous heating indicated two-step dehydration with a transition point at about 300°C (Wada et al., 1972; Wada, 1977). The weight loss measured by heating at intervals of 50°C indicated that in imogolite the OH groups are stable up to 25O"C, but that at 350 to 458°C the dehydroxylation is essentially complete (Wada and Yoshinaga, 1969). Fig. 4.7(b) shows DTA and TG curves for imogolite of established purity. Aomine and Mizota (1973) have stated that imogolite in amounts as small as 2 % of the sample can be determined by DTA utilizing the endothermic peak due to dehydroxylation.

INFRARED SPECTRA

163

4.6. INFRARED SPECTRA

Infrared spectra for mineral allophane were first published by Adler (1950). The spectra contained a broad absorption band between 800 and 1225 cm-l but showed no isolated band with a maximum at about 800 cm-l. Fig. 4.8(a) illustrates the spectral features in the region between 700 and 1400 cm-l for clays in which opaline silica, allophane, imogolite, or noncrystalline hydrous alumina and iron oxide was predominant. The spectra suggest that the absorption in this region reflects the bonding status of Si(Al)-O and/or A1-0 in the respective minerals. As described in section 4.5, Fieldes (1955) distinguished allophane A and B in

Jy

b)

(a) S~~Z/A~Z@ ratio

T-1-1 (0,s.)

Yoake 6.2

(H)

S102/A1203 ratio

1.9

1 120 Mazama

PA

(A)

2.0

2.0

(A)

108 (A)

1.7

Ki-P

(A)

1.2

1041 (A,

Id

Ki-G (Im)

1.o

Akaka

0.2

(OX)

14

12

10

x 100crn-l

8

6

905 (A, Im)

Jf ,*

KG

12 11 10 9 8

1.1

1 .o

'"

Fig. 4.8. Infrared absorption spectra (a) T-1-1 (O.S. = opaline silica- difference spectrum; Tokashiki and Wada, 1975), Mazama and Ki-P (A = allophane; Henmi and Wada, 1976), Ki-G (Im = imogolite; Henmi and Wada, 1976) and Akaka (Ox = noncrystalline hydrous alumina and iron oxides; difference spectrum; Wada and Wada, 1976). (b) Yoake (H = halloysite), PA and 108 (A = allophane), 1041 and 905 (A = allophane, Im = imogolite) and Ka-G (Im = imogolite). Recorded using DzO as the mulling medium (Wada, 1966).

164

ALLOPHANE A N D IMOGQLITE

volcanic ash-derived soils on the basis of their DTA curves. He noted from the infrared spectra that allophane B exhibits the absorption band at 800 cm-l, whereas allophane A does not. Allophane B was more common in young ashderived soils, and allophane A in older soils. On the other hand, Miyauchi and Aomine (1964) observed the 800 cm-l absorption band in 0.2-2 pm fractions, but not in the (0.2 pm fraction of certain Japanese ash-derived soils, and attributed this 800 cm-l band to cristobalite rather than allophane B. Fieldes and Furkert (1966) compared the amounts of cristobalite indicated by X-ray diffraction in various clays of New Zealand ash-derived soils with the absorbance at 800 cm-l, and concluded that the cristobalite capable of producing the X-ray diffraction was probably not the main cause of the 800 cm-l absorption band. They maintained their interpretation on the basis of the presence of allophane B as coarse-clay size, discrete, amorphous hydrous silica. Shoji and Masui (1969a) found laminar opaline silica particles in 0.2-2 pm fractions of ash-derived soils and indicated that this opaline silica had two absorption maxima in its infrared spectra at 1100 and 800 cm-l. Egawa (1961) and Fieldes and Furkert (1966) noted that the major absorption band of allophane lies in the region of 1400 to 800 cm-l, and that its absorption maximum shifts to lower frequencies with increasing maturity of the soil. This shift was attributed to differences in the dcgree of bonding between alumina and silica in allophane (Egawa, 1961), the Si02/A1203 ratio of allophane and the amounts of associated oxides (Fieldes and Furkert, 1966). Kanno et al. (1968) demonstrated that the Si-0 absorption maximum of clay and silt separates from weathered volcanic ash and pumice, shifts from 1060 to 970 cm-l with increasing Ale03 content. A similar spectrum/composition relationship has been found in fine clay fractions of three Hawaiian and one Japanese volcanic ash-derived soil by Lai and Swindale (1969) and in fine-clay samples where predominant allophane was confirmed by high resolution electron microscopy (Henmi and Wada, 1976). The latter investigators also showed that the ratio of the absorbance at 1100 cm-l to that at 940 cm-l increased with increasing Si02/A1203 ratio in the clay samples, irrespective of the predominance of allophane or imogolite. Yoshinaga and Aomine (1962b) compared the infrared spectra of imogolite and allophane and stressed their similarity. Aomine and Miyauchi (1965) expressed a similar view, but noted an additional weak band at 1140-1200 cm-l in imogolite. On the other hand, Wada (1966) found a rather clear difference between the spectra of allophane and imogolite as recorded using DzO as a mulling reagent. Fig. 4.8(b) indicates that allophanes with SiOz/A1203 ratios of 2 to 1.5 give a broad absorption band with maxima at 1010 and 945 cm-I, whereas imogolite gives an absorption band with maxima at 990,955 and 925 cm-l. Similar differences in absorption between allophane and imogolite have been noted by Russell et al. (1969) and by Wada et al. (1972). Wada (1966, 1967) interpreted the strong band of imogolite at 925 cm-l as resulting from a high proportion of

INFRARED SPECTRA

165

Si-0-A1 linkages relative to Si-0-Si, whereas Russell et al. (1969) interpreted it as indicating the presence of isolated SizO7 or SiOe groups. Russell et a/. (1969) also noted that the absorption bands near 1000, 700 and 600 cm-l in imogolite were sensitive to sample orientation. For example, when oriented on a plate, the "Si-0" stretching absorption maxima of imogolite were resolved at 990-1010 and 925-935 cm-l. They interpreted the 990-1010 cm-l band as resulting from the presence of Si-0 bonds whose vibrations were perpendicular to the fiber axis of imogolite. Ready OH-OD exchange with DzO at room temperature was found in allophane and imogolite by Wada (1966) and Russell et al. (1969). However, only partial exchange was observed for the OH groups of halloysite and montmorillonite (Wada, 1966). These observations suggest that all the OH groups and adsorbed water in allophane and imogolite are accessible to the ambient solution. That the OH groups in imogolite occur in discrete environments was suggested by Russell et af. (1969) from the multiple OH stretching vibrations appearing in a dehydrated sample. Considerable amounts of physically adsorbed water are indicated in allophane and imogolite by a fairly strong 1635 cm-1 HOH deformation band on infrared spectra. Egawa (1961) observed that the absorbance of this band decreased in samples heated at 300°C but not in those heated at lOO"C, and concluded that some water was strongly retained by allophane. Possible rehydration of the samples during KBr disc preparation and measurement was, however, not taken into consideration. Physically adsorbed water in allophane and imogolite, either HzO (Russell et al., 1969) or DzO (Wada, 1966), was considered to have been almost completely removed by heating at or above 110°C or by evacuation at room temperature. Iimura (1971) questioned this interpretation on the basis of the fact that a small absorption band at around 1630 cm-l remained on the spectra obtained by Russell et al. (1969) for allophane and imogolite which had been heated and/or evacuated. He considered this to indicate the presence of unreadily removable water in allophane. However, he overlooked that the absorption band appeared equally in allophane and imogolite which had been completely deuterated. Russell et al. (1969) compared the thermal stabilities of the OH groups of allophane and imogolite in vacuo. The OH groups in imogolite are relatively stable up to 200"C, but by 300°C about 40% dehydroxylation has occurred. On the other hand, the loss of OH groups in allophane has already begun at 15OoC,is more advanced by 25OoC, and is essentially complete by 350°C. Structural changes in allophane and imogolite on heating above 300°C have also been suggested from changes in either the OH stretching or "Si-0" stretching bands (Egawa, 1961; Egashira and Aomine, 1974; Kitagawa, 1974). Egashira and Aomine (1 974) observed that the "Si-0" absorption maximum gradually shifts from 940-1000 to 1100 cm-l in imogolite and from 1000 to 1100 cm-l in allophane on

166

ALLOPHANE AND IMOGOLITE

heating at 300°C to 9OO0C, and suggested that the Si-0-A1 bonds are disrupted upon dehydroxylation. Wada and Greenland (1970) proposed the use of difference spectra for the characterization of dissolved material obtained by dissolution treatment. In this procedure, the spectrum representing the infrared absorption of the material removed by the particular treatment was obtained by placing the sample before and the sampleafter treatment on the sampleand reference side of a spectrophotometer, respectively. This technique demonstrated the dissolution of allophanelike constituents, hydrous alumina and humus from soil clays by dithionite-citrate treatment, of allophane-like constituents by 2 % Na2C03treatment, and of allophane, opaline silica, imogolite, gibbsite, halloysite and disordered layer silicates by 0.5 N NaOH treatment (Wada and Greenland, 1970; Tokashiki and Wada, 1972; Wada and Tokashiki, 1972; Tokashiki, 1974 (quoted by Wada, 1977); Tokashiki and Wada, 1975; Wada and Wada, 1976). Fig. 4.9 gives examples of the difference spectra recorded for dithionite-citrate, 2 % Na2C03,and 0.5 N NaOH soluble fractions of two soil clays together with the ordinary spectra of the original clays and the residue remaining after 0.5 N NaOH treatment. Allophane-like constituents dissolved by dithionite-citrate and 2 % Na2C03

A'

A'

A, Im L.S.

36

28

16

14

12

x loom-I

10

8

36

28

16

14

12

10

8

X100crn-'

Fig. 4.9. Infrared spectra of W-136-8 and VH clays (modified from Wada and Tokashiki, 1972). 1 = Original clay; 2 = NazS~04-NaHC03-Na citrate soluble fraction (difference spectrum); 3 = 2% NaZC03 soluble fraction (difference spectrum); 4 = 0.5 N NaOH soluble fraction (difference spectrum); 5 = residue remaining after 0.5 N NaOH treatment. Major mineral constituents in the respective fraction: A' = allophane-like constituents; A = allophane; Ht = halloysite; Im = imogolite; L.S. = layer silicates; X = unidentified. (Wada and Tokashiki, 1972; reproduced by kind permission of Elsevier Scientific Publishing Company, the Netherlands.)

CHARGE CHARACTERISTICS

167

treatment were characterized by the “Si(A1)-0” stretching absorption band with a relatively narrow absorption maximum at 940-980 cm-I and 950-960 cm-l, respectively. The Si02/AlZ03ratios ranged from 0.2 to 0.8 for the dithionite-citrate soluble fractions and 0.4 to 1.4 for the 2 % Na2C03 soluble fractions. Additional alumina in the constituents dissolved by dithionite-citrate treatment was indicated by an absorption increase in the region from 600 to 800 cm-l. The unique absorption features of noncrystalline hydrous alumina are illustrated in Fig. 4.8(a). The allophanes dissolved in 0.5 N NaOH gave an “Si(A1)-0” stretching absorption maximum in the widest ranges of frequencies from 940 to 1050 cm-1. This variation correlates with the SiOz/A1203ratios of the 0.5 N NaOH soluble fractions; that is to say, the frequency of the absorption maximum increases with increasing Si02/A1& ratio from 0.85 to 2.5. The difference spectrum of a 0.5 N NaOH soluble fraction in which opaline silica was present in fair amounts showed absorption maxima at 1200 (shoulder), 1075, 935 (shoulder) and 790 cm-l (Fig. 4.8(a)). These frequencies are identical to those obtained for noncrystalline amorphous silica synthesized in the laboratory (Mitchell et al., 1964; Leonard et al., 1964). 4.7. CHARGE CHARACTERISTICS

The charge characteristics of a clay can be viewed as one of its structural properties. The CEC and AEC (cation- and anion-exchange capacities) measured under specified conditions are usually equated with the amounts of positive and negative charges on the clay. The CEC and AEC of volcanic ash-derived soils have also been measured due to their importance with respect to the status of “base” and plant nutrients in the soils. Birrell and Fieldes (1952) noted that the high CEC of some ash-derived soils in New Zealand is associated with the presence of allophane, but the adsorbed cations were fairly easily removed by leaching with water. They estimated that the CEC of allophanic clays is of the order 50-100 me per 100 g clay. Aomine and Yoshinaga (1955) have obtained CEC values of 23-57 me per 100 g for allophanic clays separated from Japanese ashderived soils. Birrell and Gradwell (1956), Wada and Ataka (1958) and Egawa et al. (1959) found that the CEC values of soils containing allophane measured by conventional methods vary with the concentration and pH of the leaching solution, the species of the index cation in solution and the volume and water content of the washing alcohol. Therefore, the so-called Schofield’s procedure has subsequently been used in investigations on the charge characteristics of allophanic clays. In this procedure, the CEC and AEC are determined by measuring the retention of index ions when the samples have been saturated with those ions and then equilibrated with a salt solution at an appropriate concentration and pH.

ALLOPHANE AND IMOGOLlTE

168

Excess salt is not removed by washing, and its amount is estimated by weighing. Wada and Ataka (1958) and Iimura (1966) obtained CEC values of 20-50 me and AEC values of 5-30 me per 100 g clay by equilibrating allophanic soil clays 2(( ,mi) with 0.2 N NH4C1at pH 7. They also found that the CEC increased and the AEC decreased with the pH of the equilibrating solution. Similar observations were also made by Fieldes and Schofield (1960) and Birrell (1961). Fig. 4.10 shows the effect of p t l on the CEC and AEC values of an allophanic clay as measured by limura (1966). The development of negative and positive charges in response to pH may be explained by assuming the presence of Si-OH and AlOH groups on the surface and the following reactions:

+

H+ Si-OH1Si-0AI-OH H+=AI-OHZ+

+

Wada (1977) calculated the net surface charge on this allophanic clay by using the Nernst equation relating the surface electrical potential to the pH of the equilibrium solution and the Gouy-Chapman equation relating the net surface charge to the surface potential. The value for the experimentally determined 9

8

7 0 %

6

8

a

5

@Net charge

4

ca 3 60

40

20

0

20

40

60

Positive charge

Negative charge

(rne/100g)

(me/loog)

80

Fig. 4.10. Effects of pH on the negative and positive charges of allophane ( < 2 pm; weathered pumice; SiOz/AI203 ratio = 1.43). Data: Iimura (1966). Solid line: net charge calculated using the Nernst and Gouy-Chapman equations (Wada, 1977 ; reproduced by kind permission of Soil Science Society of America, Inc., U.S.A.).

CHARGE CHARACTERISTICS

169

zero point of charge was used as a reference in the calculation. The degree of agreement between the measured and calculated values is apparent from Fig. 4.10. A gradual but substantial decrease in both CEC and AEC with decreasing concentration of the index cation and anion was noted in soils and clays containing imogolite and/or allophane (Wada and Ataka, 1958; Iimura, 1966; Wada and Harada, 1969; Wada and Okamura, 1977). This decrease, particularly at low concentrations, was ascribed to hydrolysis of adsorbed cations and anions. Ready hydrolysis suggests a stronger affinity of H+ and OH- to the exchange sites when compared with the index cation and anion. Wada and Harada (1969) also noted a cation species effect on CEC. The effect was more manifest in imogolite and allophane with a SiOz/A1203 ratio of 1.0 than in allophane with a SiOz/Al2O3ratio of 2.0. The CEC decreased in the order: Ba > Ca > K, Mg > NH4 for imogolite and allophane with a SOz/ A1203 ratio of 1.0, and the ratio of the lowest to highest CEC was 0.5 to 0.6. This effect can also be explained by assuming competition for cation-exchange sites between protons and the index cation. No comparable effects of concentration and species of index cation, or pH, were observed for the negative charge arising by isomorphous replacement within the lattice of layer silicates. An increase in the CEC of imogolite and allophane was found on raising the temperature of the solution, whereas there was a slight decrease in the AEC (Wada and Harada, 1971). The ratio of the CEC measured at 10-20°C to that a t 50-60°C was 0.36-0.59 for allophane and imogolite, 0.62-0.75 for kaolin minerals, and 0.90-0.99 for montmorillonite at pH 7.0. The increase in CEC at the higher temperature was only partially reduced on lowering the temperature again. It was suggested that this large increase in CEC includes reactions by which some “bound” functional groups are set free for ionization (Wada and Harada, 1971) and/or reactions by which A1-OH-A1 bonding is formed between two terminal Al-H20 groups (Harada and Wada, 1973). Charge development on allophane and imogolite also depends on chemical composition, specifically on the Si02/A1203ratios. There are indications that the CEC or the ratio of CEC to AEC increases with increasing Si02/A1203ratio of clays in which allophane and/or imogolite predominate (Wada, 1967; Wada and Harada, 1969; Harada and Wada, 1973). This accords with the mechanism of charge development inferred from the effects of pH on CEC and AEC. Egawa et a/. (1959) found that the CEC of an allophanic clay decreased remarkably on air-drying or heating at 105°C when the CEC was measured using various reagents, e.g. 0.5 N NH4CH3CO0 and 80% C2H50H, for washing. Iimura (1966) and Kubota (1973) found that previous heating of allophanic clays a t 105°C resulted in an increase in the CEC and a decrease in the AEC. Harada and Wada (1974) found that the CEC increase on drying over P205 or heating a t 105”C, amounted to 30-50% of the CEC of the undried sample. This result

170

ALLOPHANE AND IMOGOLITE

was interpreted as showing that negative charge develops on dehydration, possibly due to changes in the coordination of some surface A1 atoms. Some supporting evidence has been provided by measurements of surface acidity (section 4.8), and by the electrophoresis of allophanic clays (section 4.9). Iimura (1 966) claimed success in estimating the “absolute CEC” of allophanic clays using 0.2 N Ba(OH)2.A sample from which exchangeable cations had been removed was shaken in 0.2 N Ba(0H)Z. The consumption of Ba(OH)2 on the reaction represented the “absolute CEC”. The measured values for allophanic clays ranged from 480 to 670 me per 100 g clay, and were equated with the number of surface Si-OH groups. The Na content of fine clays (<0.2 pm) containing imogolite and/or allophane and treated with hot 2 % NaZC03was in the range of 80 to 250 me per 100 g (Wada, 1967). Aomine and Jackson (1959) proposed the use of the “CEC delta value” for estimating the allophane in soils and clays. One soil or clay sample treated with HZOZand dithionite-citrate is treated with hot 2 % NazC03 solution, and another is treated with hot NaCH3COO solution at pH 3.5. The CEC values are then determined by a conventional method, and the difference is taken as the delta value. The delta values found for several allophanic clays ranged from 83 to 111 me per 100 g, whereas those for kaolinite, halloysite and montmorillonite were 0, 18 and 10 me per lOOg, respectively. 4.8.

SURFACE ACIDITY

The pH dependence of CEC and ready hydrolysis of adsorbed cations indicate the high affinity of cation-exchange sites of allophane and irnogolite to protons, and therefore their weak acidity. Seki (1926) noted that “there are many ash loams which are neutral, notwithstanding they are extremely unsaturated with alkaline bases”. Iimura (1966) found that the pH of electrodialyzed suspensions of allophanic clays ranged from 4.0 to 6.5 and that these suspensions showed little or no exchange acidity. The latter finding was interpreted in terms of a balance between exchange acidity and alkalinity. Yoshida (1970, 1971) treated allophane, imogolite and crystalline layer silicate clays with 1 N AlCh and determined the exchangeable A1 and H on these clays. All the exchange sites on allophane and imogolite were occupied by H, and not by Al, whereas more than 60% of the exchange sites in the crystalline layer silicates were occupied by Al. This result indicates that the strength of all acid sites on allophane and imogolite is lower than that of the AI(HZO)~~+ which dissociates,

+

A1(H20)s3+~A1(Hz0)~(OH)~+ H+, with a dissociation constant of about 1.0 x On the other hand, an increase in acidity or proton-donating properties of the

ELECTROPHORESlS AND DISPERSION-FLOCCULATION

171

I I I I I m m m m m Ho 4.0106.8

3.3t04.0

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1

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Temp. (OC)

(a) Acid strengths of H(A1) or Na saturated clays kept at various relative humidities. (b) Acid strengths of H(A1) or Na saturated clays air-dried at room temperature and heated at different temperatures. A = allophane, Gb = gibbsite, Ht = halloysite, 1m = imogolite, Kt = kaolinite, Mt = montmorillonite. (Henmi and Wada, 1974; reproduced by kind permission of the Mineralogical Society, England.) Fig. 4.11.

ALLOPHANE A N D IMOGOLITE

172

clay surface with decreasing water content has been demonstrated by several investigators (Mortland, 1970). Benesi (1956) showed that the acid strength of air-dried montmorillonite and kaolinite as well as synthetic aluminosilica gels can be estimated by examining the colors of pH indicators adsorbed onto the clays in non-polar solvents. Yamamoto (1960) reported that air-dried samples of allophanic materials did not impart an acid color to butter yellow in isooctane, whereas the preheated samples did give an acid color. Henmi and Wada (1974) determined the acid strength of allophane and imogolite by observing the coloration of indicators in benzene, and compared the results with those for gibbsite, halloysite, kaolinite and montmorillonite. Fig. 4.1 l(a), (b) shows the acid strength of these clays saturated with H(A1) or Na and kept at various relative humidities and heated at different temperatures, respectively. Ho, as a measure of acidity, is related to the pK, (the negative logarithm of the acid dissociation constant) of the indicator as follows: HO = pKa log (B)/(A), where (B) and (A) are the concentrations of the base and acid forms of the indicator. The larger the Ho value, the weaker is the surface acidity that the clay surface exhibits. The measured weakest and strongest acid strengths correspond to the strengths of 8 X lo-* to 5 X lop5% and 71 to 90 ”/, sulfuric acid, respectively. Fig. 4.1 I(a), (b) indicates that H(A1)-saturated allophane behaves as a strong acid in a relatively dry environment, but its acid strength is very much reduced either by increasing its water content or by saturating it with Na. Imogolite shows only a very weak acidity under medium-dry to moist conditions. A marked enhancement in acidity is observed in allophane and imogolite after they have been dried over PzO5 (r.h. 0 %; Fig. 4.1l(a)) or heated sufficiently to cause dehydroxylation (Fig. 4.11(b)). H(A1)-saturatedmontmorillonite, kaoliniteand halloysite show stronger acidities than allophane and imogolite in a relatively moist environment. Heating the respective clays at higher temperatures results in various changes in acidity (Fig. 4.1 l(b)). This probably reflects changes in structure caused by dehydroxylation or transformation to different mineral phases.

+

4.9. ELECTROPHORESIS A N D DISPERSION-FLOCCULATION

The electrokinetic properties and stability of clay suspensions are important in clay technology. They are, however, complex subjects which do not readily lend themselves to elementary treatment. Certain of the relevant facts concerning clays and soils containing allophane and imogolite will be presented in this section. Shioiri (1934, 1935) determined the isoelectric point of soil clays separated from undried soils of various origins by observing their electrophoresis or electroosmosis. The isoelectric point of clays separated from “siliceous” soils was below pH 3.5, whereas that for clays separated from “aluminous” soils was in

COORDINATION STATUS OF ALUMINUM

173

the range of pH 3.7 to 7.5. He also found that the isoelectric point of one “aluminous” soil clay fell from pH 8.4 to 3.0 on predrying of the sample. Watanabe (1966) observed a similar effect in allophane, but Horikawa (1975a) did not do so. The increase in net negative charge on drying has also been inferred from CEC and AEC data (section 4.7). Sadzawka et al. (1972) observed that the pH of Chilean volcanic ash soils suspended in 0.01 M NaaS04 fell by about 0.5 pH unit or more after the soils had been dried at 110°C. Horikawa (1975a) found that imogolite began to flocculate as the pH was increased beyond 7 to 7.5. The pH at which imogolite had no charge was 9 to 10, and the electrophoretic mobility then remained at zero up to pH 12, where the imogolite began to dissolve. That imogolite did not exhibit negative charge in electrophoresis in alkaline media may be correlated with the location of SiOH groups on the inner side of its tube unit, as proposed by Cradwick et al. (1972) (see Fig. 4.13, below). As expected from the charge and electrophoretic characteristics of allophane and imogolite, the pH of the medium is important for ensuring stability in allophane and imogolite dispersion. An alkaline medium (NaOH; pH 10) can be used for allophane with an SiOz/A1203ratio of 2 or higher, whereas an acid medium (HCI; pH 4) is required for imogolite and allophane with lower SOz/ A1203 ratios. Kamoshita and Yumura (1951) recommended the use of acetic acid for maintaining suspensions of ash-derived soils at pH 5.0 during dispersion. Kanno (1961) found that HaOa-treatedsoils containing allophane dispersed better in acid media than alkaline media or media containing calgon (sodium hexametaphosphate), although soils containing considerable amounts of layer silicates in addition to allophane did disperse in alkaline media. Kobo et al. (1974) confirmed this observation by comparing the dispersion of soil clays with different allophane and layer silicate contents using media containing HCl and calgon. Aomine and Egashira (1968) showed that at pH 4.5-6.5, the flocculation of allophane with electrolytes is determined primarily by the valence of the anions and that of montmorillonite by the valence of the cations. Horikawa (1975b) reported similar observations, and found that both citrate and lauryl sulfate are more effective anions than sulfate as flocculating agents for allophane. Aomine and Egashira (1968) have proposed the use of the ratio between the flocculation values of CaClz and Na2S04 for differentiating the predominating surface charge of soil colloids. Values of 20-30 were obtained for soil clays in which allophane and imogolite predominated, whereas values of 0.04-0.12 were found for soil clays with layer silicates or humus. 4.10. COORDINATION STATUS OF ALUMINUM

The coordination status of aluminum in allophane has been discussed in

174

ALLOPHANE AND IMOGOLITE

relation to the origin of negative charges (Fieldes and Schofield, 1960) and the development of surface acidity (Birrell, 1962). These investigators suggested a 4-fold coordination for some of the aluminum in allophanic clays. X-ray fluorescence spectroscopy was subsequently used to obtain data on the coordination number of aluminum in allophanic clays. The analysis is based on the fact that the emission wave length of the A1-Ka line of aluminum is dependent on its coordination. Egawa (1964) and Udagawa et al. (1969) separated allophanic clays from a pumice bed. Their samples differed in SiOz/A1203ratio (2.37 and 1.67) but were alike in coordination status, about 50-60% of the aluminum being estimated to be in a 4-fold coordination at room temperature and at about 200OC. Okada et al. (1975) analyzed two allophanic soil clays with SiOz/A1~03 ratios of 1.37 and 1.64 and one precipitated “allophane” with an SiOz/A1203 ratio of 0.25. They gave A1 coordination numbers of 5.8, 5.8 and 5.5 for these samples by X-ray fluorescence spectroscopy, and 5.5, 6.0 and 6.0 by analysis of their radial distribution curves. Data on the content of imogolite, volcanic glass and other impurities in the samples examined were not given in the above studies. Henmi and Wada (1976) later made similar analyses of clay samples which differed in allophane, imogolite and volcanic glass content, and in particle size. The data indicated that the aluminum in imogolite is only in the 6-fold coordination, whereas the aluminum in allophane is in both the 4- and 6-fold coordinations. The AI(IV) content of allophane increases with increasing SiOz/AI2O3ratio and amounts to 50 % of the total aluminum in samples with a SiO2/AI2O3ratio of close to 2.0, The higher AI(1V) content of coarse clays compared to fine clays of the same origin indicates the influence of unweathered volcanic glass in which nearly all the aluminum is in the 4-fold coordination. It was concluded that a high proportion of Al(IV) atoms must be a key structural feature of allophane, and that allophane probably inherits aluminum in the 4-fold coordination from volcanic glass. The potential CEC values of allophanes calculated from their Al(IV) content were in the range of 200 to 400 me per 100 g clay (see Table 4.4, below). A partial neutralization of this negative charge by protons was suggested to explain the much smaller CEC values measured for allophane. 4.11 . ANION SORPTION

Strong sorption of phosphate has been recognized as an important feature of volcanic ash-derived soils. Seki (1926) noted that their “absorptive power” of phosphoric acid is usually very strong, and the acid applied as soluble phosphate is liable to be converted into a form unavailable to plants. Colloidal alumina and ferric oxides were, however, considered to be present in the soils and to be responsible for this phosphate fixation. Egawa et al. (1957) compared the yields of barley grown on soils of different clay mineral composition which had

ANION SORPTION

175

received variable amounts of phosphate. The different responses among the soils were correlated with the differences in their phosphate sorption. The values for allophanic soils were 2610-3070 mg P205/100 g soil and those for soils in which illite and/or kaolin minerals predominated, were 940 and 1070 mg Pz05/ 100 g soils. Aomine and Yoshinaga (1955) determined the phosphate retention by repeated washing with 1 M ammonium phosphate at pH 7.0 in allophanic clays ((2 pm). The high phosphate retention (307-402 mmole P per 100 g clay) and very low ratio of CEC to phosphate retention (0.065-0.186) were considered to characterize allophane. Wada (1959) studied the reaction of 1 M ammonium phosphate with allophanic clays. The phosphate sorption after a 24-hr reaction at pH 4 and room temperature was in the range of 430 to 520 mmole per 100 g clay. A considerable amount of NH4, ranging from 310 to 460 mmole per 100 g clay, was also retained. After 3 weeks, the apparent retentions of phosphate and ammonium increased to 1330 and 610 mmole per 100 g clay, respectively. X-ray analysis and microscopic observations indicated that the allophane was almost completely converted to a new aluminum phosphate, “ammonium-substituted taranakite”. The reaction was retarded at pH 7.0. Although occurring at a slower reaction rate, halloysite also combined with ammonium phosphate to form “taranakite”. Yoshinaga and Yamaguchi (1970) studied the adsorption of polyphosphates by allophanic clays. The finding that allophane did not form any crystalline products even after 6 months contact with polyphosphate solutions at 1 M P and pH 4.0, was emphasized. Studies of anion adsorption on goethite have shown that “specific” adsorption in addition to “non-specific” adsorption of anions occurs in soils (Hingston et al., 1967, 1968). The non-specific adsorption refers to adsorption of anions by simple coulombic interaction with positive charges on AI-OH2+ or Fe-OH2+ groups, while the specific adsorption refers to incorporation of anions in the coordination shell of an Fe or A1 atom as a ligand. There is no doubt that both non-specific and specific adsorption of phosphate occurs on allophane and allophane-like constituents. The latter, specific adsorption is also likely to induce decomposition of these aluminosilicates and precipitation of new aluminum phosphates, so that overlapping of the different reactions renders the obtainment of a well-defined adsorption maximum difficult, even at suitable pH. Kato (1970a,b) measured phosphate sorption in A and B horizon samples of volcanic ash-derived soils before and after successive treatment with HzOz, dithionite-citrate and Tamm’s reagent. Reduction in phosphate sorption was more marked after H2Q2and/or dithionite-citrate treatment than after treatment with Tamm’s reagent. He suggested an important role for sesquioxidic constituents which were dissolved by dithionite-citrate treatment in phosphate sorption rather than allophane. The adsorption isotherm of phosphate for an ashderived soil before and after dithionite-citrate treatment has been determined by Miyauchi and Nakano (1971). The original sample showed a Freundlich-type

176

ALLOPHANE AND IMOGOLITE

isotherm and did not give an adsorption maximum even at 0.5 M P, whereas the sample after dithionite-citrate treatment showed a Langmuir-type adsorption isotherm and exhibited an adsorption maximum at 0.1 M P. The latter was attributed to monolayer adsorption of phosphate on allophane. The estimated contribution of the dithionite-citrate soluble components to the phosphate sorption reached about 50% at 0.5 M P. The importance of dithionite-citrate soluble “sesquioxidic” components in phosphate sorption by volcanic ashderived soils was also indicated from measurements of the so-called “phosphate fixation capacity” (Yoshida and Miyauchi, 1975; Yoshida and Kanaya, 1975). In the investigations described above, it was assumed that the dithionitecitrate treatment dissolved “sesquioxidic” components only from soils containing allophane. However, as indicated in section 4.6, allophane-like constituents are also dissolved by the treatment. Dissolution of aluminum and iron but not of allophane-like constituents was found only for soils containing humus or gibbsite in large amounts but no allophane (Mizota and Aomine, 1975a,b; Tokashiki and Wada, 1975). Therefore, the phosphate sorption by ash-derived soils is attributed to either allophane, imogolite, allophane-like constituents or Al(Fe)-humus complexes. Anions other than phosphates can be specifically adsorbed by allophane. Kawaguchi et al. (1954) noted that 0.5 M NaF extract of a soil containing a high amount of “active” aluminum showed a marked alkaline reaction (>pH lo). The reaction was represented as AI(OH)3

+ 6 NaF = Na3AlF6 + 3 NaOH

The OH release upon reaction with 2-3 M NH4F was found to be as high as 1100 mmole per 100 g clay for allophane, whereas it was 250 and 300 mmole per 100 g clay for montmorillonite and kaolinite (Egawa et al., 1960). Ammonium-substituted cryolite, (NH&AIFc, was formed from allophane but not from kaolinite. Birrell (1961) studied the reactions of allophane with phosphate, molybdate, chromate, vanadate, sulfate and fluoride solutions, and found that in most cases the products were noncrystalline. However, acid phosphate and neutral or acid fluoride solutions gave high yields of crystalline products. Interest in the reaction of aluminum hydroxide with fluoride was revived when Fieldes and Perrott (1966) proposed the use of this reaction as a field test for allophane. For the test, a small amount of the soil sample (about 30 mg) is placed on phenolphthalein paper with one drop of 1 M NaF. The soil then turns the paper red if its allophane content is appreciable. This test is useful, but it is important to bear in mind that the reagent will react with any available aluminum associated with hydroxyl or other ligands. Brydon and Day (1970) showed that the Bf horizon of podzols containing a large amount of extractable aluminum component but no allophane, gave a positive test. Bracewell et al. (1970) and Perrott et al. (1976) have attempted to measure the OH release at constant

ANION SORPTION

177

pH and to utilize this as a measure of the relative amounts of poorly ordered inorganic material in soils. The adsorption of monomeric silica at concentrations not exceeding 100 ppm SiOz has been studied with soils containing imogolite and/or allophane, or halloysite (Wada and Inoue, 1974). The adsorption of silica increased with increasing pH from 6 to 10, suggestingthat silicate anions are specifically adsorbed onto these minerals. All adsorption isotherms conformed to Freundlich’s equation above certain SiOz concentrations, below which the zero points of silica adsorption were found at SiOz concentrations ranging from 2.5 to 26 ppm, the value being dependent on the pH and soil type. This result suggested that the soluble silica equilibria in the soils were governed largely by the precipitation-dissolution equilibria of the clay minerals. The approximate silica adsorption capacities of allophane-imogolite and halloysite at pH 8-9 were estimated to be 10-25 g and 2.5 g of SiOz per 100 g of clay, respectively. Allophane and imogolite are effective in the adsorption of organic anions as well as inorganic anions. Thus, acetate is adsorbed non-specifically up to the AEC of these clays, while citrate, a strong ligand for aluminum, is more strongly adsorbed and in greater amounts. In addition, van der Waals interactions contribute to the adsorption of high molecular weight organic anions. Much greater adsorption of humified clover extract by allophane and imogolite than by montmorillonite and halloysite has been demonstrated and the mechanism of interaction between this newly formed humus and imogolite studied by Inoue and Wada (1968, 1971a,b). Accumulation of humus constitutes one important feature in the volcanic ash-derived soils known as Ando Soils (Thorp and Smith, 1949), Andepts (Soil Survey Staff, 1960) or Humic Allophane Soils (Kanno, 1962). As reviewed by Wada and Harward (1974), the important role of allophane and imogolite in the accumulation of humus has been suggested on the basis of their reactivity with organic compounds. Kyuma and Kawaguchi (1964), Kumada and Kato (1970) and Kumada and Ohta (1974) have demonstrated that allophane exhibits a catalytic effect on oxidative changes in polyphenols adsorbed onto it. On the other hand, Kato (1970b) pointed out the importance of dithionite-citrate soluble sesquioxides, particularly alumina, in the accumulation of humus in Ando soils. Tokashiki and Wada (1975) observed the accumulation of considerable amounts of humus in certain A1 horizons of ash-derived soils in which allophane and imogolite were absent or nearly absent. Wada and Higashi (1976) obtained a good linear correlation between the amounts of humus and aluminum (both extractable with 0.1 M Na4P207)for a number of Ando soils, irrespective of the presence or absence of allophane. These observations suggest that one essential component which stabilizes organic matter against biotic degradation and leaching is aluminum, though this does not exclude the possibility that allophane, imogolite and allophane-like constituents also contribute to the accumulation of humus.

178

ALLOPHANE A N D IMOGOLITE

4.12. SURFACE AREA

A high specific surface area has been considered characteristic of noncrystalline clay materials. Gradwell and Birrell (1954) described that allophane resembles montmorillonite in possessing a large total surface area as measured by glycol desorption, but unlike montmorillonite this surface area remains unchanged after ignition at 650°C. Aomine and Yoshinaga (1955) and Egawa et al. (1955) determined the ethylene glycol retention of allophanic soil clays and obtained retention values of 85-236 and 39-90 mg/g clay for samples heated at 100 and 600°C, respectively. Kinter and Diamond (1960) noticed that the glycerol retention of a Japanese Ando soil sample was reduced to about half its original value when heated at 600°C, whereas it remained unchanged before and after saturation with triethylammonium ion. They considered that the surface area of allophane was entirely external. Greenland and Quirk (1962) found that the surface area of allcphane as measured by cetyl pyridinium bromide (CPB) adsorption from an aqueous solution was considerably less than the area determined by nitrogen adsorption. Their interpretation was that much of the surface exists in stable pores too small to accommodate a double layer of CPB molecules on opposing surfaces. Aomine and Otsuka (1968) measured the surface areas of allophanic soil clays by various methods. Adsorption of polar liquids such as glycerol, ethylene glycol monoethyl ether (EGME) or water, gave surface areas of about 500 m”g. Cationic compounds such as CPB and o-phenanthroline gave zero or very small values for the surface area, probably being affected by the predominant positive charge on the allophane surface. The surface area derived from nitrogen adsorption was almost one-third of that measured with the polar liquids. Based on these data, they concluded that the size of the allophane particles should be less than 50 8,in diameter if they are spherical and that aggregation upon drying and heating reduces the accessibility of nitrogen molecules to the surface. An aggrement between the surface area of allophane calculated from the particle size (55 A in diameter) and density (1.9) and that measured with glycerol (600 m”g) was also reported by Kitagawa (1971). On the other hand, Egashira and Aomine (1974) gave EGME surface areas of 700-900 m2/g and 900-1100 mz/g for allophane and imogolite, respectively. The samples had been freeze-dried and then vacuum-dried over P z O ~They . also found that oven-drying and exposure to moist air affected EGME retention in allophane and imogolite, but did not in montmorillonite. Wada and Harward (1974) suggested an area of about 700 m2/g for imogolite using data on the adsorption of water vapor (Yoshinaga, 1968; Wada and Yoshinaga, 1969; Wada and Henmi, 1972). In all the estimations described above, the cross-sectional area of the polar molecule adsorbed on allophane and imogolite was assumed to be equal to that adsorbed on montmorillonite. The formation of a monolayer with such adsorbates as glycerol and EGME was also tacitly assumed. Both assumptions were

DENSITY AND POROSITY

179

however, unwarranted. Wada and Harward (1974) calculated the surface area of imogolite to be 1400-1500 m2/g using values for the inner and outer diameters of its tube unit of 7-10 and 17-21 A and a density of 2.65 g/cm3. It may be concluded that the cross-sectional area occupied by each EGME and water molecule on imogolite is probably higher than that on montmorillonite by as much as 40 and loo%, respectively. 4.13. DENSITY AND POROSITY

Eirrell and Fieldes (1952) reported values for the density of allophanic soil clays ranging from 1.98 to 2.37, but gave no description of the method used. Aomine and Yoshinaga (1953) obtained values of 2.32-2.35 for coarse volcanic glass fragments separated from a volcanic ash-derived soil by the pycnometer method. The density given by Winchell and Winchell (1959) for allophane in coal and ore deposits was 1.85-1.89. Gradwell (1955) made density determinations by displacement with water and toluene in clayey subsoils which differed in their clay mineral compositions. The values obtained for an allophanic soil with water and toluene were 2.37 and 2.03, respectively. The corresponding values for soils containing crystalline layer silicates were 2.57-2.79 and 2.56-2.73. Kitagawa (1971) also determined the density of five allophanic clays by displacement with water, and reported values ranging from 1.89 to 1.93. On the other hand, Takagi and Aboshi (1955) examined the effect of the remanent air in soil samples on the measured density of powdery material and noted that this effect was particularly marked in volcanic ash-derived soils. The measured density was 2.45 and 2.75, when displacement with water was carried out at pressures of 300-760 and 30-1 mm Hg, respectively. Wada and Yoshinaga (1969) reported that the density of imogolite determined by displacement with water was 2.6-2.75. This high density was taken as an indication of dense atomic packing in the structure unit, and hence, of the crystallinity of imogolite. Wada and Wada (1977) measured the density of two allophanes ((0.2 pm), imogolite (gel film), kaolinite (<2 pm), halloysite (<2 pm), montmorillonite ( t 2 ym) and volcanic glass (0.2-0.02 mm) by displacement with water. The results are shown in Table 4.3. The high density of allophane was interpreted as indicating that in this mineral, water molecules have easy access to pores and interatomic spaces which might be present in its structure, and effectively fill them up. The density of imogolite (Wada and Yoshinaga, 1969), allophane and layer silicates (Wada and Wada, 1977) was also determined by a float-sink test using mixtures of acetylene tetrabromide, C2H2Br4,and appropriate organic liquids. The values obtained were less than those obtained by displacement with water (Table 4.3). The differences in value increased in the order: volcanic glass, kaolinite < metahalloysite < halloysite < montmorillonite < allophane, imogo-

1so

ALLOPHANE AND IMOGOLITE

TABLE 4.3. Density data for allophane, imogolite, volcanic glass, kaolinite, halloysites and montmorillonite (Wada and Wada, 1977) Mineral Allophane Allophane Imogof i te Volcanic glass Kaolinite Metahalloysite Hal foysite Montmorillonite

Density by displacement with water

CWs0H

CH3COCH3

C6Hs

cc14

2.78 2.72 2.70 2.44 2.65 2.53 2.53 2.72

1.84 1.84 1.70 2.39 2.54 2.33 2.17 1.98

1.94 1.98 1.94 2.39 2.57 2.46 2.16 1.98

2.35 2.35 I .98 2.38 2.59 2.46 2.42 2.32

2.39 2.35 2.33 2.40 2.59 2.49 2.46 2.42

Density by float-sink tests in c2HzBr.1 and

lite. The lower density measured by the float-sink test in the last four minerals was interpreted by Wada and Wada (1977) in terms of the adsorption of polar molecules such as water, methanol and acetone on the surfaces of the minerals, which was confirmed by infrared spectroscopy. This adsorption may or may not be associated with the presence of micropores or interlayer spaces in the minerals, but there is cxcIusion of C2H2Br4molecules from the space where the polar molecules are adsorbed. If allophane consists of hollow spherules as indicated by electron microscopy (section 4.3), the very similar density values of samples suspended in benzene, C6H6,and carbon tetrachloride, CC14, which are markedly different in density, i.e. 0.879 vs. 1.595 g/cm3, suggests that no C&&3or CC14 would be retained in preference to C2H2Br4,and that only water would be retained in the interior of the spherules. Wada and Henmi (1972) correlated the maximum retention of quaternary ammonium chlorides and water by imogolite with its micropore space. They estimated that the porosity in the air-dried imogolite amounts to 55-60% of the total volume, and roughly 50 and 25 % of the total porosity belong to the interand intra-tube-unit pores, respectively. 4.14.

STRUCTURE MODELS

Predictions of the behavior of clays and their application in practice are severely limited by a lack of accurate knowledge of structure. Thus, attempts have been made to develop structure models for allophane and imogolite. Fieldes (1966) considered that the formation of allophane from volcanic ash is due to structural randomness in the volcanic glass and imperfect structures in the component feldspars. Fieldes and Furkert (1966) expressed the opinion that clay-size ground feldspar or hydrous glasses may be regarded as allophane.

STRUCTURE MODELS

181

Wada (1967) reviewed the available data on soil allophane including imogolite, and suggested two end-members with the chemical compositions, 2Si02.A12033H20 and Si02.A1203.2H20, and a structural scheme common to the two endmembers and intermediate compositions. The proposed structure consisted of silica tetrahedral and alumina octahedral chains in which corners of the tetrahedra and octahedra were shared. Iimura (1969) calculated an average structural formula for allophanes by equating the Ba(OH)2 titer with the number of OH groups bonded to silicon and by assuming that the aluminum in allophane is entirely in the 6-fold coordination. The formula was found to be (OH)$. dY1.6&

330%

23A12(0H)114.77,

where (0H)I and (0H)II represent OH groups bonded to Si and Al, and OI and OII represent oxygen in Si-0-Si and Si-0-A1 bonds, respectively. Udagawa et al. (1969), on the basis of thermal and X-ray fluoresence measurements, suggested that allophane may have a kaolin-like layer structure rather than a chain structure and that part of the aluminum in allophane is in the 4-fold coordination. Brindley and Fancher (1970) then considered various kaolin defect structures to yield a composition for allophanes generally containing less silica and more water with respect to alumina than kaolinite. They compared the calculated compositions of such defect structures with the vacant Si sites and compositions of allophanes given by Yoshinaga (1966) and suggested that the defects are more likely to be large, clustered defects than small, dispersed ones. A kaolin-like layer structure model for allophane has also been proposed by Okada et a!. (1975) on the basis of X-ray radial distribution, X-ray fluoresence and nuclear magnetic resonance analysis. Their kaolin-like layer structure has vacant Si sites in the tetrahedral sheet in alumina-rich allophane and vacant A1 sites in silica-rich allophanes. No discussion of structure-morphology relationships was given by the investigators who considered allophane to have a kaolin-like layer structure, However, as described in section 4.3, high resolution electron microscopy suggested the possibility that allophane consists of “hollow spherules” with diameters of about 50 A. The wall thickness was estimated to be 10 A or less. Fig. 4.12 gives a schematic cross-section of the probable structure unit of allophane and its structural features (Wada and Wada, 1977). The atomic arrangement in the wall has not yet been elucidated, but the latter may be constructed from defect layer structures consisting of an A1-0, OH octahedral sheet and an Si, AI-0, OH tetrahedral sheet. Table 4.4 shows the number of Si and A1 atoms allocated to the kaolin layer structure on the basis of the chemical and X-ray fluorescence spectroscopy of four allophane samples (Henmi and Wada, 1976). The results indicate that more defects can be expected in the octahedral sheet than the

ALLOPHANE AND IMOGOLITE

182

W\

D z O Z HO

OHZ?DzO

-

strongly retained

H20 ”Defect layer structures” Al-0, OH octahedra sheet

(

SI, ACO, OH tetrahedra sheet

“Pores”

$ 23 A

35-55i-

Fig. 4.12. A schematic representation of the “hollow”, spherical structure unit of allophane. (Wada and Wada, 1977; reproduced by kind permission of the Mineralogical Society; England).

tetrahedral sheet. The defects would cause curling of the sheet, and large clustered vacant sites would provide openings in the wall, as indicated by the ease of complete OH-OD exchange (section 4.6) and the density measurements (section 4.13). The openings would not be limited to one in each spherule, as shown in Fig. 4.12, and would admit free entry of small molecules such as water. The presence of strongly retained water in the void space inside the wall was also indicated by the density measurements. As shown in Table 4.4, the presence of A1 atoms in the tetrahedral sheet results in the creation of negative charge. Partial neutralization of this negative charge by protons and a coordination change of the A1 atoms responding to changes in hydration and pH, have been suggested by Henmi and Wada (1976) to explain the CEC data of allophane. Earlier electron optical studies of imogolite (Russell et al., 1969; Wada and Yoshinaga, 1969) indicated that it has a chain structure with a repeat distance of 8.4 A along the chain axis. The two proposed structures were similar in assigning this 8.4 A repeat distance to a gibbsite-like chain or ribbon, but differed in their assessment of the number and state of the silicate anions attached to it. TABLE 4.4. Number of Si and AI atoms allocated to the kaolin layer structure, and the calculated value of the potential CEC of allophane (Henmi and Wada, 1976) Sample: genesisl)

Tetrahedral spaces

Octahedral spaces

Potential CEC2) (me/100 g)

Al 3.55 225 2.38 362 1.81 376 1.44 393 1) Abbreviations: W.P., weathered pumice; W.V.A., weathered volcanic ash. 2) The potential CEC value was calculated by using an average value (2.5) for the molar HzO(+)/ Also3 ratios of allophane and imogolite (Wada and Yoshinaga, 1969), and by assuming that one unit of negative charge is created by every AI(1V) atom. Ki-P: W.P. Ku-P: W.P. PA: W.P. VA: W.V.A.

Si 2.82 2.42 2.52 2.56

Al 1.18 1.58 1.48 1.44

STRUCTURE MODELS

183

The two structures did not account for the tubular feature of the structure unit which was established later from electron microscopic studies. The most recent version of the imogolite structure to be advanced is that of Cradwick et al. (1972), who took into account its tubular morphology (section 4.3) and the presence of isolated orthosilicate anions (section 4.1). Part of the postulated cylindrical structure unit is shown schematically in Fig. 4.13. It has a circumference of 10, 11, or 12 gibbsite unit cells, with gibbsite b along the circumference and gibbsite a parallel to the cylinder axis. Each orthosilicate anion displaces H from the three OH groups surrounding a vacant octahedral site in a gibbsite sheet. The fourth Si-0 bond points away from the sheet and is neutralized by a proton to form an Si-OH group. This structure requires a considerable shortening of the 0-0 distance around the vacant octahedral site. It was considered that this contraction may account for the shortening of the repeat distance from 8.6 A in gibbsite to 8.4 A in imogolite and also for the curling of the gibbsite sheet to form a cylinder. The outside diameters of the cylinders range from 18.3 to 20.2 A, which is consistent with estimates from electron micrographs (17 to 21 A; section 4.3). The composition of the resulting structure is (OH)3A1203SiOHor SiOz.AI203.2Hz0. This composition was com-

k-

7L

Al

gibbsite b imogolite a r / n -

u-

!- - - n -(Jn - -. -?

a

T

b

d

Fig. 4.13. (a) Postulated relationship between the structure unit of imogoiite and gibbsite. The S O H groups which would lie at the cell corners in imogolite are omitted from the diagram. (b) Curling of the gibbsite sheet induced by contraction of one surface to accommodate Si030H tetrahedra; projection along the imogolite c axis. (Cradwick et al., 1972; reproduced by kind permission of Macmillan Journals Ltd., England.)

184

ALLOPHANE AND IMOGOLITE

pared with the 1.1 SiOz.AI2O3.2.3-2.8 HzO given by Wada and Yoshinaga (1969). Fourier transforms of the three proposed structures projected perpendicular to the cylinder axis showed fairly good agreement with the most detailed electron diffraction pattern of imogolite. The infrared spectra and ease of complete OH-OD exchange with D20 (section 4.6), the very weak surface acidity (section 4.8), unique electrokinetic phenomenon (section 4.9), 6-fold coordination of aluminum (section 4.10), and retention of quaternary ammonium chlorides (section 4.13), can also be accounted for by the proposed structure. REFERENCES Adler, H. H. (1951) Prel. Rept. No. 6 Amer. Petrol. Inst. Pro,. 49, Columbia Univ. Aomine, S. (1958) J. Sci.Soil Manure Japan 28, 508. Aomine, S. and Egashira, K. (1968) Soil Sci. Plant Nutr. (Tokyo) 14,94. Aomine, S. and Jackson, M. L. (1959) Soil Sci.Soc. Amer. Proc. 23, 210. Aomine, S. and Mizota, C. (1973) Proc. Intern. Clay Conf. Madrid 1972, 207. Aomine, S. and Miyauchi, N. (1965) Soil Sci. Plant Nutr. (Tokyo) 11, 212. Aomine, S. and Otsuka, H. (1968) Trans. 9th Intern. Congr. Soil Sci., 1, 731. Aomine, S. and Wada, K. (1962) Amer. Minerl, 47, 1024. Aomine, S. and Yoshinaga, N. (1953) Sci.Bull, Far. Agr. Kyushu Univ. 14, 257. Aomine, S. and Yoshinaga, N. (1955) Soil Sci. 79, 349. Askenasy, P. E., Dixon, J. B. and McKee, T. R. (1973) SoilSci. SOC.Amer. Proc. 37,799. Bates, T. F. (1971) The Electron Optical Investigation of Clays (ed. J. A. Gard), p. 109-157, Mineralogical Society (Clay minerals group). Benesi, H. A. (1956) J. Anier. Chem. Soc. 78, 5490. Birrell, K. S. (1961) New ZealandJ. Sci. 4, 393. Birrell, K. S. (1962) New Zealand J . Sci. 5 , 453. Birrell, K. S. and Fieldes, M. (1952) J. Soil Sci. 3, 156. Birrell, K. S., Fieldes, M. and Williamson, K. I. (1955) Amer. Miner. 40, 122. Birrell, K. S. and Gradwell, M. (1956) J. Soil Sci.7, 130. Bracewell, J. M., Campbell, A. S. and Mitchell, B. D. (1970) Clay Miner. 8, 325. Brindley, G. W. and Fancher, D. (1970) Proc. Intern. Clay Conf. Tokyo 1969,2,29. Brown, G. (1955) Clay Miner. Bu/I. 2, 294. Brydon, J. E. and Day, J. H. (1970) Canad. J . Soil Sci. 50, 35. Chukhrov, F. B., Berkhin, S . I., Ermilova, L. P., Moleva, V. A. and Rudnitskaya, E. S. (1964) Proc. Intern. Clay Conf. Stockholm 1963, 2, 19. Cradwick, P. D. G., Farmer, V. C., Russell, J. D., Masson, C. R., Wada, K. and Yoshinaga, N. (1'372) Nature Pkyr. Sci.240, 187. Egashira, K. and Aomine, S. (1974) Clay Sci.4,231. Egawa, T. (1961) Advances in Clay Science, vol. 3, p. 103, Gihodo. Egawa, T. (1964) Clay Sci. 2, 1. Egawa, T. and Sato, A. (1960) Advances in Clay Science, vol. 2, p. 384, Gihodo. Egawa, T., Sato, A. and Nishimura, T. (1960) Advances in Clay Science, VOI. 2, p. 252, Gihodo. Egawa, T., Sekiya, K. and limura, K. (1957) Bull. Natl. Inst. Agr. Sci. (Tokyo) B7, 31. Egawa, T. and Watanabe, Y. (1964) Bull. Natl. Inst. Agr. Sci. (Tokyo) B14, 173. Egawa, T., Watanabe, Y . and Sato, A. (1955) Bull. Natl. Znsf. Agr. Sci. (Tokyo) B5, 39. Egawa, T., Watanabe, Y. and Sato, A. (1959) Advances in Clay Science, vol. I , p. 260, Gihodo. Eswaran, H. (1972) Clay Miner. 9, 281. Fey, M. V. and LeRoux, J. (1975) Proc. Intern. Clay Conf. Mexico City 1975, 451. Fieldes, M. (1955) New Zealand J. Sci. Tech. 37, 336. Fieldes, M. (1966) New Zealand J. Sci. 9, 599. Fieldes, M. and Furkert, R. J. (1966) New Zealand J. Sci. 9, 608.

REFERENCES

185

Fieldes, M. and Perrott, K. W. (1966) New Zealand J. Sci. 9, 623. Fieldes, M. and Schofield, R. K . (1960) New Zealand J. Sci. 3, 563. Gotz, J. and Masson, C. R. (1971) J. Chem. SOC.A, 686. Gradwell, M. W. (1955) New Zealand J. Sci. Tech. 37, 283. Gradwell, M. and Birrell, K. S. (1954) New Zealand J. Sci. Tech. 36, 108. Greenland, D. J. and Quirk, J. P. (1962) Trans. Intern. SOC.Soil Sci. Comm., IV, V 79. Grim, R. E. (1968) Clay Mineralogy, McGraw-Hill. Harada, Y . and Wada, K. (1973) Soil Sci. Plant Nutr. (Tokyo) 19, 73. Harada, Y . and Wada, K. (1974) Trans. 10th Intern. Congr. Soil Sci., 2, 248. Hashimoto, I. and Jackson, M. L. (1960) Clays Clay Miner. 7, 102. Henmi, T. and Wada, K. (1974) Clay Miner. 10,231. Henmi, T. and Wada, K. (1976) Amer. Miner. 61, 379. Higashi, T. and Ikeda, H. (1974) Clay Sci. 4, 205 Hingston, F. J., Atkinson, R. J., Posner, A. M. and Quirk, J. P. (1967) Nature 215,1459. Hingston, F. J., Atkinson, R. J. and Posner, A. M. (1968) Trans. 9th Intern. Congr. Soil Sci., 1 , 669. Horikawa, Y . (1975a) Clay Sci. 4, 255. Horikawa, Y . (1975b) Clay Sci. 4, 271. Iimura, K. (1966) Bull. Natl. Inst. Agr. Sci. Japan B17, 101. Iimura, K. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 161. Iimura, K . (1971) Dojo Hiryo no Kenkyu (Japanese) 2, 56. Jnoue, T. and Wada, K. (1968) Trans. 9th Intern. Congr. SoiI Sci., 3, 289. Inoue, T. and Wada, K. (1971a) Clay Sci. 4, 61. Inoue, T. and Wada, K . (1971b) Clay Sci. 4, 71. Jackson, M. L. (1956) Soil Chemical Analysis-Advanced Course, published by the Author, Madison, Wisconsin, p. 72-74. Kamoshita, Y . and Yumura, Y . (1951) J. Sci Soil Manure Japan 22, 33. Kanno, I. (1959) Advances in Clay Science, vol. 1, p . 213, Gihodo. Kanno, I . (1961) Bull. Kyushu Agr. Expt. Sta. 7, 1. Kanno, I. (1962) Trans. Int. SOC.Soil Sci. Comm., IV, V 422. Kanno, I., Kuwano, Y .and Honjo, Y . (1960) Advances in Clay Science, vol. 2, p. 355, Gihodo Kanno, I., Onikura, Y . and Higashi, T. (1968) Trans. 9th Intern. Congr. Soil Sci., 3, 111. Kato, Y . (1970a) J . Sci. Soil Manure Japan 41, 218. Kato, Y . (1970b) Pedologist 14, 16. Kawaguchi, K. (1975) Kagaku (Japanese) 45, 586. Kawaguchi, K., Fukutani, H., Murakami, H. and Hattori, T . (1954) Bull. Res. Inst. Food Sci. Kyoto Univ. 14, 82, Kinter, E. B., and Diamond, S. (1960) Clays Clay Miner. 7, 125. Kitagawa, Y . (1971) Amer. Miner. 56, 465. Kitagawa, Y . (1974) Arner. Miner. 59, 1094. Kobo, K., Oba, Y . and Oishi, K. (1974) J. Sci. Soil Manure Japan 45, 8. Kohyama, N. and Sudo, T. (1975) Clays C/ay Miner. 23, 215. Kubota, T . (1973) Dojo Hiryo no Kenkyu (Japanese) 4, 37. Kumada, K. and Kato, H. (1970) Soil Sci. Plant Nnfv. (Tokyo) 16, 195. Kumada, K. and Ohta, S. (1971) Quat. Res. 10, 151. Kurabayashi, S. and Tsuchiya, T. (1960) Advances in Clay Science, vol. 2, p. 178, Gihodo. Kuwano, Y . and Matsui, T. (1957) Misc. Rept. Res. Inst. Nut. Resources (Tokyo) 45, 33. Kyuma, K. and Kawaguchi, K. (1964) Soil Sci. Soc. Amer. Proc. 28, 371. Lai, S. H. and Swindale, L. D. (1969) Soil Sci. Soc. Amer. Proc. 33, 804. Leonard, A., Suzuki, S., Fripiat, J. J. and De Kimpe, C. (1964) J. Phys. Chem. 68, 2607. McKeague, J. A,, Brydon, J. E. and Miles, N. M. (1971) Soil Sci. Soc. Amer. Proc. 35,33. Mehra, 0. P. and Jackson, M. L. (1960) Clays Clay Miner. 7,317. Minato, H . (1960) Advances in Clay Science, vol. 2, p. 350, Gihodo. Mitchell, B. D., Farmer, V. C. and McHardy, W . J. (1964) Advan. Agron. 16, 327. Miyauchi, N. and Aomine, S. (1964) Soil Sci. Plant Nutr. (Tokyo) 10, 199. Miyauchi, N. and Aomine, S . (1966a) Soil Sci. Plant Nutr. (Tokyo) 12, 13. Miyauchi, N. and Aomine, '3. (1966b) Soil Sci. Plant Nutr. (Tokyo) 12, 187.

.

186

ALLOPHANE AND IMOGOLITE

Miyauchi, N. and Nakano, A. (1971) Bull. Fac. Agr. Kagoshima Univ. 21, 143. Miyazawa, K. (1966) Bull. Natl. Inst. Agr. Sci. Japan B17, 1. Mizota, C. and Aomine, S. (1975a) Soil Sci. Plant Nutr. (Tokyo) 21, 93. Mizota, C. and Aomine, S. (1975b) Soil Sci. Plant Nutr. (Tokyo) 21, 201. Mizota, C. and Aomine, S. (197%) Soil Sci. Plant Nutr. (Tokyo) 21, 327. Mortland, M. M. (1970) Advan. Agron. 22, 75. Nagasawa, K. (1969) Proc. Intern. Clay Conf. Tokyo 1969,1, 15. Noishiki, Y. and Tazaki, K. (1975) Pap. Inst. Thermal Spring Res. Okayama Univ. 44, 1. Nozawa, K. (1953) Misc. Rept. Res. Inst. Nat. Resources 30, 56. Okada, K., Morikawa, S., Iwai, S., Ohira, Y. and Ossaka, J. (1975) Clay Sci. 4,291. Ossaka, J. (1960) Advances in C h y Science, vol. 2, p . 339, Gihodo. Ossaka, J. (1962) Advances in Clay Science, vol. 4, p. 33, Gihodo. Perrott, K. W., Smith, B. F. L. and Inkson, R. H. E. (1976) J. Soil Sci. 27, 58. Ross, C. S. and Kerr, P. F. (1934) US.Geol. Survey Prof. Pap. 185G, 135. Russell, J. D., McHardy, W. J. and Fraser, A. R. (1969) CZay Miner. 8, 87. Sadzawka, R. M. A,, Melendez, A. E. and Aomine, S. (1972) Soil Sci. Plant Nutr. (Tokyo) 18, 191. Schwertmann, U. (1964) Z. Pflanzenernaehr. Deung. Bodenk. 105, 194. Seki, T. (1926) Proc. 3rd Pan-Pacific Sci. Congr., 2, 1936. Shinagawa, A. (1962) Bull. Fac. Agr. Kagoshima Univ. 11, 155. Shioiri, M. (1934) Nippon Gakujutsu Kyokai Hokoku (Japanese) 10, 694. Shioiri, M. (1935) Trans. 3rd Intern. Congr. Soil Sci., 3, 70. Shioiri, M. (1952) Dojo-Hiryogaku Kowa (Japanese), p . 1-26, Asakura Shoten. Shoji, S. and Masui, J. (1969a) Soil Sci. Plant Nutr. (Tokyo) 15, 161. Shoji, S. and Masui, J. (1969b) Soil Sci. Plant Nutr. (Tokyo) 15, 191. Shoji, S. and Masui, J. (1971) J. Soil Sci. 22, 101. Soil Survey Staff (1960) Soil Classification,a Comprehensive System, 7th Approximation, Soil Conservation Service, United States Department of Agriculture, p. 139-141. Sudo, T. (1953) Miner. J. 1, 66. Sudo, T. (1954) Clay Miner. Bull. 2, 96. Sudo, T. (1959) Mineralogical Study on Clays of Japan, p . 149-193, Maruzen. Sudo, T. (1974) Nendokobutsugaku (Japanese), p. 309-326, Iwanami Shoten. Sudo, T. and Nakamura, T. (1952) Amer. Miner. 37, 618. Sudo, T. and Takahashi, H. (1956) Clays Clay Miner. 4, 67. Takagi, S. and Aboshi, H. (1951) Rep. Inst. Sci. Tech. Univ. Tokyo 5, 253. Tazaki, K. (1971) Geol. Soc. Japan J. 77, 407. Tazaki, K. (1975) J. Clay Sci. Soc. Japan 15, 3. Thorp, J. and Smith, G. D. (1949) Soil Sci. 67, 117. Tokashiki, Y. and Wada, K. (1972) Clay Sci. 4, 105. Tokashiki, Y. and Wada, K. (1975) Geoderma 14, 47. Tsuzuki, Y. and Nagasawa, K. (1960) Advances in Clay Science, vol. 2, p. 377, Gihodo. Uchiyama, N., Masui, J. and Shoji, S. (1968) J. Sci. Soil Manure Japan 39, 149. Udagawa, S., Nakada, T. and Nakahira, M. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 151. Wada, K. (1959) Soil Sci. 87, 325. Wada, K. (1966) Soil Sci. Plant Nutr. (Tokyo) 12, 176. Wada, K. (1967) Amer. Miner. 52, 690. Wada, K. (1977) Minerals and Their Roles in the Soil Environment (ed. J. B. Dixon), p. 603-638. Soil Sci. Soc. Arner. Inc. Wada, K. and Ataka, H. (1958) Soil Plant Food (Tokyo)4, 12. Wada, K. and Greenland, D. J. (1970) Clay Miner. 8, 241. Wada, K. and Harada, Y. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 561. I Soil . Sci. 22, 109. Wada, K. and Harada, Y. (1971) . Wada, K. and Harward, M. E. (1974) Advan. Agron. 26, 211. Wada, K. and Henmi, T. (1972) Clay Sci. 4, 127. Wada, K., Henmi, T., Yoshinaga, N. and Patterson, S. H. (1972) Clays Clay Miner. 20, 375. Wada, K. and Higashi, T. (1976) J. Soil Sci. 27, 357. Wada, K. and Inoue, A. (1974) Soil Sci. Plant Nutr. (Tokyo) 20, 5. Wada, K. and Kubo, H. (1973) Abstr. Pap. Soc. Sci. Soil Manure Japan 19, 37.

REFERENCES

187

Wada, K. and Matsubara, I. (1968) Trans. 9th Intern. Congr. Soil Sci., 3, 123. Wada, K. and Okamura, M. (1977) Proc. Intern. Seminar, Soil Environment and Fertility Management in Intensive Agriculture, p. 811, SOC.Sci. Soil Manure Japan. Wada, K. and Tokashiki, Y. (1972) Geoderma 7, 199. Wada, K. and Wada, S. (1976) Geoderma, 16, 139. Wada, K. and Yoshinaga, N. (1969) Amer. Miner. 54, 50. Wada, K., Yoshinaga, N., Yotsumoto, H., Ibe, K. and Aida, S. (1970) Clay Miner 8, 487. Wada, S. and Wada, K. (1977) Clay Miner., 12, 289. Watanabe, T. (1968) Amer. Miner. 53, 1015. Watanabe, Y. (1966) Bid. Natl Inst. Agr. Sci. Japan B16, 91. White, W. A. (1955) Amer. Miner. 38, 634. Winchell, A. N. and Winchell, H. (1959) Elements of Optical Mineralogy, Part II., John Wiley and Sons. Yamamoto, D. (1961) Clay Sci. 1, 32. Yoshida, M. (1970) J. Sci. Soil Manure Japan 41,483. Yoshida, M. (1971) J. Sci. Soil Manure Japan 42, 329. Yoshida, M. and Kanaya, H. (1975) J. Sci. Soil Manure Japan 46, 143. Yoshida, M. and Miyauchi, N. (1975) J. Sci. Soil Manure Japan 46, 89. Yoshinaga, N. (1966) Soil Sei. Plant Nutr. (Tokyo) 12, 47. Yoshinaga, N. (1968) Soil Sci. Plant Nutr. (Tokyo)14,238. Yoshinaga, N. and Aomine, S. (1962a) Soil Sci.Plant Nutr. (Tokyo) 8(2), 6. Yoshinaga, N. and Aomine, S. (1962b) Soil Sci. Plant. Nutr. (Tokyo)8(3), 22. Yoshinaga, N. and Yamaguchi, M. (1970) Soil Sci. Plant Nutr. (Tokyo) 16, 121. Yoshinaga, N., Yotsunioto, H. and Ibe, K. (1968) Amer. Miner. 53, 319.

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Chapter 5 Kaolin minerals

Keinosuke NAGASAWA

Kaolin minerals occur widely as products of hydrothermal alteration and weathering and as constituents of sediments. Their distribution, modes of occurrence and properties, and the interrelationships between them have been the subject of many studies. These minerals are important raw materials for the ceramic, paper, and other industries, and are mined in many places. The economically important kaolin deposits have been summarized by Muraoka et al. (1958), Nagasawa et al. (1969), Fuji (1976), Minato (1976), and Nagasawa (1976). In this Chapter, a general review of the occurrence and properties of kaolin minerals, not restricted to those found in economically important deposits, is given together with a discussion of their genesis. The kaolin minerals dealt with here consist of kaolinite, dickite, nacrite, and halloysite. The nomenclature for halloysite has been a matter of dispute for many years. As described below, the present author (Nagasawa and Miyazaki, 1976) showed that all halloysites examined by him were in a fully hydrated state if they were examined without prior drying. This seems to confirm the opinion of Bates (1952) that halloysite (2Hz0) can be formed only by the dehydration of halloysite (4Hz0). In this article, therefore, the name halloysite is used to denote the 10 A material. 5.1.

DICKITE AND NACRITE

5.1 .I. Occurrence

Dickite and nacrite have been most frequently reported from the so-called “Roseki” deposits. In Japan, especially in its western part, there are many Roceki deposits. These were formed as a result of hydrothermal alteration of various rocks, mainly acidic and intermediate volcanic and pyroclastic rocks of Cretaceous to Miocene age, and consist mainly of pyrophyllite and quartz often associated with kaolin minerals, diaspore and muscovite, although in some cases the kaolin minerals predominate over the pyrophyllite. Four kaolin minerals, kaolinite, dickite, nacrite and halloysite, have been reported from these deposits. Yoshiki (1934) first identified the kaolin mineral in the Shokozan area, Hiro189

190

KAOLIN MINERALS

shima Prefecture, as dickite on the basis of its optical and thermal properties. The Roseki deposits of the Shokozan area were later studied by Iwao (1949), Matsumot0 (1968), etc. According to them, they represent stratiform deposits formed by replacement of Cretaceous dacite and dacitic tuff, and consist of a pyrophyllite zone and an overlying kaolin-alunite-quartz zone, both of which are surrounded by a zone of silicification containing hematite and pyrite (Fig. 5.1). Dickite occurs in the kaolin-alunite-quartz zone as lenticular masses or veins sometimes associated with nacrite, diaspore, or alunite (Takeshi, 1958; Iwamoto, 1963; Matsunioto, 1968).

Silicification zone impregnated with Fe minerals

Pyrophyllite zone

--

Corundum-diaspore-pyrophyllite

Alunite-Kaolin zone

zone

a

Silicification zone Weakly altered wall rock

Fig. 5.1. Schematic cross-section showing the alteration zoning at the Shokozan mine, Hiroshima Prefecture. The iron mineral in the silicificationzone impregnated with Fe minerals is usually hematite in the zone on the hanging wall, and pyrite in that on the footwall. (After Matsunioto, 1968.)

Dickite has also been reported from many other Roseki deposits, e.g. Takatoku, Tochigi Prefecture (Kodama, 1963); the Kanakura and Kobayashi mines, Nagano Prefecture (Iwai et al., 1949; Takeshi, 1958); the Hiraki mine (Tanaka et al., 1963), Ebara mine (Ueno, 1964; Yamamoto, 1965), Kiyotaki mine (Ueno, 1964), Shinagawa-Sampo mine (Takeshi, I958 ; Ueno, 1964) and Fukuyama mine (Takeshi, 1958; Ueno ef al., 1958), Hyogo Prefecture; and the Rissho mine (Yamamoto, 1965) and Kato mine (Mitsuishi area) (Sugiura and Nakano, 1960), Okayama Prefecture. In these cases, the dickite usually occurs as fillings in the interstices of aggregates of diaspore, as veinlets, or as massive aggregates. Nacrite is also found in Roseki deposits, both associated and not associated with dickite. Examples include the Otoge mine, Yamagata Prefecture (Tanemura and Horiuchi, 1958); Takatoku, Tochigi Prefecture (Kodama, 1963); the Kobayashi and Yonago mines, Nagano Prefecture (Iwaj et al., 1949; Takeshi,

DICKITE AND NACRITE

191

1958); the Ebara mine (Yamamoto, 1965) and Shinagawa-Sampo mine (Takeshi, 1958), Hyogo Prefecture; and Shokozan area, Hiroshima Prefecture (Takeshi, 1958; Iwamoto, 1963). Occurrences of dickite and nacrite due to younger volcanic activity have been recognized. The kaolinization often occurred in association with alunite or silica deposits and with sulfur deposits of both Quaternary and Pliocene age. A typical example of these deposits is seen in the Ugusu mine, Shizuoka Prefecture, as shown in Fig. 5.2 (Iwao, 1962, 1968; Uno and Takeshi, 1977). Here, silica deposits were formed by hydrothermal alteration due to former geothermal activity in a period after the Pliocene. Zonal alteration, i.e. silica zone (central part)+alunite zone-+clayey zone+original rock (Miocene propylite) is well developed, and dickite represents a principal component of the inner portion of the clayey zone sometimes in association with nacrite. Dickite has been reported from the Itaya mine, Yamagata Prefecture, where it occurs in altered pyroclastics composed of quartz, alunite and kaolin minerals (Honda, 1964; Togashi and Fujii, 1972; Togashi, 1976). Nacrite, associated with dickite, is also known from the Itaya mine area (Honda, 1964). In an active geothermal area at Otake, Oita Prefecture, dickite occurs as a constituent of an alteration zone characterized by kaolin and pyrophyllite (Hayashi, 1973). At the Kasuga and Akeshi mines, Kagoshima Prefecture, nacrite and dickite have been reported to occur in association with gold mineralization (Tokunaga, 1954, 1955, 1957). Here, stockwork and impregnation deposits of gold, enargite, luzonite, pyrite, etc. are found in a zone of silicification which is surrounded by a dickite zone and then a kaolinite zone. The nacrite occurs as veinlets without metallic minerals and as a minor constituent of the dickite zone. Other examples of dickite occurrence associated with metallic mineralization have been reported

400-

Am1 I I l l I I l l I I

1

/.

.:

0-..-O-

100

200,

Silica zone

n

Altrnite zone

Ix_I Propytite

Clayey zone

Fig. 5.2. Cross-section of the silica deposit at the Ugusu mine, Shizuoka Prefecture. (After Iwao, 1970.)

KAOLIN MINERALS,

192

TABLE 5.1 Chemical analysis data of dickite SiOz TiOz Ah03 Fez03 FeO MnO MgO CaO NazO KzO HzO+ HzO Ig. loss Total SiOz/A1203

Hokugo 45.62 38.92 1.03 tr. 0.12 0.08

Mitsuishi

Ebara

45.42 0.02 38.78 0.88 0.04

45.31 0.00 40.17 0.14

Shokozan 45.99 0.21 39.34 0.01

] 13.98

0.86 0.12 tr. tr. 13.42 0.54

0.00 tr. 0.00 0.24 0.01 13.89 0.35

99.75

100.08

100.11

14.45 100.06

1.99

1.99

1.91

1.98

0.06

-

Hokugo: Hokugo-mura, Miyazaki Prefecture (Matsukuma and Tanaka, 1955). Mitsuishi: Kato mine, Mitsuishi, Okayama Prefecture (Sugiura and Nakano, 1960). Ebara: Ebara mine, Hyogo Prefecture (Ueno, 1964). Shokozan: Shokozan mine, Hiroshima Prefecture (Matsumoto, 1968).

TABLE 5.2 Chemical analysis data of nacrite SiOz TiOz A1203 Fez03 FeO MnO MgO CaO NazO KzO HzO HzOTotal

+

Yonago 41.52 tr. 37.51 1.59 0.92 0.92 0.64

14.54 0.93 98.57

Otoge

Kanagato

44.52 tr. 39.91 0.09 0.01

45.17 0.04 40.24 0.02

0.42 0.14 0.03 0.08 14.34 0.93 100.47

tr. 0.30 0.40 0.06 0.12 14.13 0.10 100.58

1.90 1.88 1.89 SiOziA1~03 Yonago: Yonago mine, Nagano Prefecture (Twai era!., 1949). Otoge: Otoge mine, Yamagata Prefecture (Tanemura and Horiuchi, 1958). Kanagato: Kanagato mine, Yamaguchi Prefecture (Minato, 1976).

KAOLINITE AND HALLOYSITE

193

from stibnite veins at Hokugo, Miyazaki Prefecture (Matsukuma and Tanaka, 1955), a gypsum-anhydrite vein at the Oe lead-zinc mine, Hokkaido (Urashima and Sato, 1967; Nagasawa et al., 1976), Sn-W veins at the Akenobe mine, Hyogo Prefecture (Nagasawa et al., 1976), and the wall rock of the hematite ore at the Akatani iron mine, Niigata Prefecture (Imai, 1960). Nacrite has also been reported from the Kanagato copper mine, Yamaguchi Prefecture, where it occurs as veinlets in kaolinized wall rocks (Minato, 1976). Sugiura and Nakano (1960) have reported dickite at Tomi near Omi, Niigata Prefecture, where it fills a cavity in limestone associated with a small amount of quartz. On the walls of the cavity, the limestone has become transluscent due to recrystallization. 5.1.2. Mineralogical properties Chemical analysis data for dickite and nacrite are given in Tables 5.1 and 5.2, respectively. All the listed samples have smaller values for the molar SiOz/Ale03 ratio than ideal. Examples of X-ray powder diagrams of dickite and nacrite are given in Fig. 5.3. They show the characteristic patterns of these minerals. Takeshi (1958) has pointed out that there is a variation in structural integrity in dickite: that accompanied by diaspore tends to have more ordered structure. Infrared absorption spectra for dickite and nacrite from the Shokozan area are shown in Fig. 5.4. Kodama and Oinuma (1963) and Oinuma and Hayashi (1968) reported that nacrites from near Takatoku and from the Kasuga mine show essentially the same spectral features as in the figure. According to the latter authors, the OH stretching absorptions for the Takatoku material have frequencies of 3700, 3649, and 3629 cm-l, among which the last is the most intense. 5.2. KAOLINITE AND HALLOYSITE

5.2.1. Occurrence: hydrothermal

Kaolinite is an important hydrothermal mineral and occurs abundantly in hydrothermally altered rocks. The Roseki deposits mentioned in section 5.1.1 contain kaolinite as an ixportant constituent. In the Roseki deposits of the Mitsuishi area, Okayama Prefecture, the largest Roseki mining area in Japan, kaolinite occurs in ciose association with pyrophyllite and sometimes with diaspore, and forms massive bodies or veins in ordinary Roseki composed of pyrophyllite and quartz (Kimura, 1951;Yamamoto, 1959, 1965). Some other Roseki deposits consist mainly of kaolinite instead of pyrophyllite, the latter being absent or not important

194

A

ic 20

KAOLIN MINERALS

25

35

40

2 E (CuKa)

Fig. 5.3. X-ray diffraction diagrams of nacrite from the Yonago mine, Nagano Prefecture (A) and dickite from the Shokozan mine, Hiroshima Prefecture (B). (After Nagasawa et nl., 1969.)

in them. The Hiraki mine (Tanaka et al., 1963) and Ebara mine (Ueno, 1964; Yamamoto, 1965), Hyogo Prefecture, are examples. At the Yuri mine, Hyogo Prefecture, halloysite occurs as veins in kaolinite-type Roseki (Ando, 1952). “Toseki”, an important raw material for pottery in Japan, is composed of quartz, muscovite and/or kaolinite. Well-known Toseki deposits occur in the Amakusa Islands, Kumamoto Prefecture, where rhyolite dykes have been altered to Toseki. Togashi (1974) revealed the following zoniilg in one of the Amakusa deposits : carbonate zone (core of the dyke)+clay mineral zone-+ silicification zone+wealdy altered zone (margin of the dyke). All four zones contain muscovite, usually interstratified with expandable layers, and kaolinite.

KAOLINITE AND HALLOYSITE

195

Wave number (crn-')

40

:

36

x 102

12 I

I I

A

"\; dr

i

Y-

1

4 I

I

Fig. 5.4. Infrared absorption spectra of nacrite (A) and dickite (B), both from the Shokozan mine, Hiroshima Prefecture. (By courtesy of H. Takeshi.)

Toseki deposits are also known at Izuhara in the Tsushima Islands, Nagasaki Prefecture. In this case, they represent bleached quartz porphyry. White clay composed of kaolinite, halloysite and quartz occurs abundantly as fillings of fissures in the Toseki (Yajima et al., 1970). Kaolinite commonly occurs in altered rocks related to young volcanic activity. Examples include the Itaya mine, Yamagata Prefecture (Togashi and Fujii, 1972; Minato, 1976; Togashi, 1976), the Seta mine, Hokkaido (Komura and Sudo, 1976), the Ugusu mine, Shizuoka Prefecture (Iwao, 1962, 1968; Uno and Takeshi, 1977) (Fig. 5.2), the Beppu mine, Oita Prefecture (Kinoshita and Muta, 1953), Ibusuki, Kagoshima Prefecture (Muraoka, 1951), and the Otake geothermal area, Oita Prefecture (Hayashi, 1973), where kaoljnite is found in association with quartz, cristobalite, or alunite. The Itaya mine is the largest paper clay mine in Japan. The deposits were formed by the alteration of Pleistocene volcanic and pyroclastic rocks as a result of Pleistocene volcanic activity,

196

KAOLIN MINERALS

although Togashi (1976) has shown from radiometric age determinations that in one of the deposits, a basement Miocene tuff is exposed which was altered hydrothermally to muscovite, kaolinite and interstratified micalsmectite in the Miocene. Many volcanic sulfur deposits are known in Japan, especially in northeastern Honshu and Hokkaido. Examples include the Matsuo mine, Iwate Prefecture; Zao mine, Yamagata Prefecture; and the Abuta mine, Hokkaido. They represent replacement deposits composed of iron sulfides and native sulfur and are surrounded by the following alteration zones: a silica or opal zone (inner), alunite zone, kaolin zone, and smectite zone (outer). The kaolin zone consists of kaolinite and halloysite associated with opal (Kinoshita and Muta, 1954; Mukaiyama, 1959; Takeuchi, Takahashi and Abe, 1966). Although the total width of the alteration zones usually reaches scores of meters, more condensed examples are often observed along fissures in compact lava flows. One case is illustrated in Fig. 5.5.

0

5m

Fig. 5.5. Alteration zoning along a fissure in the Nishiazuma sulfur mine, Yamagata Prefecture. 1, Sulfur zone; 2, pyrite zone; 3, opal zone; 4,alunite zone; 5,6, kaolin zone; 7, unaltered rock. (After Mukaiyania, 1959.)

Several hydrothermal halloysite deposits are known. At the Joshin mine, Gunma Prefecture, Quaternary andesite breccia has been altered to tubular halloysite with small amounts of opal and tridymite (Minato and Kato, 1961). At the Iki mine on Iki Island, Nagasaki Prefecture, stratiform halloysite deposits were formed by selective hydrothermal alteration of vitric pyroclastics intercalated in Quaternary basalt flows. The halloysite has a spherical shape (see Fig. 5.12, below) and is associated with cristobalite. The overlying and underlying wall rocks have been weakly altered to form chlorite and smectite (Fujii, 1961; Minato and Utada, 1969). Other examples of hydrothermal halloysite deposits have been reported from the Omura mine, Nagasaki Prefecture (Naga-

KAOLINITE A N D HALLOY SITE

197

sawa et al., 1969), the Okuchi mine, Kagoshima Prefecture (Fujii, 1962; Minato, 1975,1976), and the Rangoshi mine, Hokkaido (Muraoka and Tanemura, 1954). The deposits at the last mine also contain kaolinite. Mitsuda (1960a) found halloysite in the marginal part of a hydrothermal bentonite deposit at Itoigawa, Niigata Prefecture. Halloysite is also known from amygdales in volcanic rocks. Ishibashi (1974) described its occurrence together with zeolites in amygdales in basalt at two localities in Saga Prefecture. Occurrences of kaolinite in altered rocks related to metallic mineralization have been reported from several mines. The Kasuga mine mentioned above is one case. Another important example is the Kampaku mine, Tochigi Prefecture, where gold-quartz veins exist in rhyolite. After the gold mineralization, extensive kaolinization occurred and a silicification zone was formed around the kaolinized rock. The intensely kaolinized rocks have been mined for kaolin clay, which is composed mainly of kaolinite associated with minor amounts of halloysite, alunite, etc. (Mutoh, 1952; Tanemura, 1954). As mentioned above, the hematite replacement deposits of the Akatani mine, Niigata Prefecture, are accompanied by kaolinized wall rocks (Imai, 1960). Kaolinization is also present in the wall rocks of copper-lead-zinc veins at the Mikawa mine near Akatani. Here, the mineralization may be divided into two stages : an earlier sulfide-quartz stage, and a later hematite-carbonate stage. The wall-rock alteration related to the later stage is characterized by kaolinite, quartz, muscovite and siderite (Nagasawa, 1961). At the Mikawa mine, kaolinite occurs also in the veins themselves as fillings of interstices and as veinlets in the sulfide-quartz ore. This kaolinite is closely associated with siderite (Nagasawa, 1953, 1961). Other examples of the occurrence of kaolinite in metallic veins have been reported from the Konomai gold-silver mine, Hokkaido (Urashima, 1953), the Kawaguchi copper mine, Akita Prefecture (Honda and Shiikawa, 1957), the Isobe-Koyama gold-copper mine, Yamagata Prefecture (Isobe et al., 1967), the Toyoha lead-zinc mine, Hokkaido (Shikazono, 1975), etc. In the above examples, the kaolinite is not associated closely with metallic sulfides other than iron sulfides. However, a close association of kaolinite with sphalerite and pyrite has been reported by Sudo and Hayashi (1957), Sudo et al. (1958) and Hayashi (1961) from the Hanaoka mine, Akita Prefecture, and the Kamikita and Aomori mines, Aomori Prefecture, where kaolinite, diaspore, and pyrophyllite (only at Kamikita and Aomori) occur in and around “Kuroko”-type ore bodies. Shirozu et al. (1972) have reported the occurrence of kaolinite, dickite and nacrite in association with black ore (lead and zinc) and pyrite ore in a Kuroko deposit at Matsumine (Hanaoka mine). The occurrence of kaolinite in altered rocks related to Kurokotype deposits has also been reported by lijima (1972a) and Kimbara and Nagata (1 974). Kaolinite occurrence in close association with metallic mineralization is

198

KAOLIN MINERALS

known in certain mercury deposits. Takubo et al. (1954) reported kaolinite as an important constituent of cinnabar veins and their wall rocks in the Yamato mercury mine, Nara Prefecture. Fujiwara and Kujirai (1972) reported cinnabar impregnation in kaolinized sandstone at the Ryushoden mine, Hokkaido. 5.2.2. Occurrence: weathering and sedimentary

Kaolinite is an important product of weathering. In fact, kaolin minerals are the most abundant and widely distributed constituents of Japanese soils (Matsui, 1959; Aomine, 1969). Most soils apart from the volcanic ash soils described in Chapter 2 contain a kaolin mineral as their dominant constituent. Although halloysite with spherical or tubular morphology has been reported in soil (Watanabe et al., 1969), the form of the kaolin mineral in soils is usually platy. Such platy kaolin has sometimes been referred to as metahalloysite due to its low structural integrity (Matsui, 1959; Kato, 1964/65; Nagasawa, 1966). However, the platy morphology suggests that it may be kaolinite. Verification of this will require further detailed mineralogical examinations. In the deeper portions of the zone of weathering, on the other hand, halloysite is a dominant product of weathering. In this case, percolating water is responsible. Shimizu (1972b) examined several weathering profiles of granitic rocks and quartz porphyry, and found that halloysite is the dominant clay mineral in saprolites in contrast to surface soils which are rich in kaolinite. The halloysite has the shape of long tubes. Nakagawa et al. (1972) showed that the feldspar in saprolite from quartz diorite at Senmaya, Iwate Prefecture, had been altered to halloysite. Nagasawa (1966) and Ichiko (1971) examined the clay mineral composition of the Upper Pleistocene marine sand constituting coastal terraces near Nagoya, Aichi Prefecture. The clay fraction of the sand was originally composed of kaolinite, illite and smectite, but it had been altered to tubular halloysite in places where the sand came in contact with percolating water. On the other hand, biotite is known to have been altered to kaolinite associated with hydrobiotite and vermiculite-chlorite intergrades in granitic saprolites (Kakitani and Kono, 1972; Shimizu, 1972b). Kaolinite has also been reported from weathered rocks of various geological ages. At the Iwate clay mine, Iwate Prefecture, the Cretaceous welded tuff underlying Oligocene fresh-water sediments was weathered to a redbed composed mainly of kaolinite, associated in part with gibbsite (Iijima, 1972b). In the area around Nagoya, the basement granite underlying Pliocene sedimentary kaolin deposits was weathered and kaolin minerals were formed from feldspars (Hukuo and Kutina, 1960; Fujii, 1968; Nagasawa and Kunieda, 1970; Shimizu, 1972a). The kaolin minerals consist of platy kaolinite in some places and of long tubular halloysite associated with small amounts of platy kaolinite in others. Both minerals sometimes occur together even within a single exposure (Shimizu, 1972a). The situation at Kakino, Gifu Prefecture, is illustrated in Fig. 5.6. What controls the differential distribution of kaolinite and halloysite is not yet known. The

199

KAOLINITE AND HALLOYSITE

0

6 1

Granite

0

HalbysiU

Fig. 5.6. Distribution of clay minerals in weathered granite under Pliocene “Gaerome” clay at the Kakino mine, Toki, Gifu Prefecture. The amount of clay minerals was estimated by X-ray diffrao tion. (After Shimizu, 1971.)

biotite in the original granite was weathered to kaolinite. The latter is pseudomorphous after the biotite, and is sometimes elongated perpendicular to the basal plane to give a vermicular shape (Mitsuda, 1960b). Studies on the clay minerals in recent marine sediments around the Japanese Islands have been summarized by Oinuma and Kobayashi (1966), Oinuma (1969), and Aoki et a/. (1975). Kaolinite occurs widely as a minor constituent, although the amounts are larger in sediments of the East China Sea (Kobayashi and Oinuma, 1965). The sediments of Lake Shinji, a brackish lake in Shimane Prefecture, have been examined by Fujii and Yasuda (1971). They showed that kaolinite is the dominant clay mineral. Relatively little work has been done on the clay mineralogy of Paleozoic sediments. The studies of Oinuma and Kobayashi (1963) and Nishiyama et al. (1973) showed that kaolinite is rare in such sediments. However, kaolinite-rich red shales have been reported by Igo (1961) from a Carboniferous formation at Fukuji, Gifu Prefecture. These shales overlie limestone disconformably and are considered to have been derived from lateritic materials. Extensive studies on the clay mineralogy of argillaceous rocks of the Cretaceous and Tertiary have been carried out by Aoyagi et al. (1975, 1976). Kaolinite was found to be dominant in argillaceous sediments in brackish and neritic environments and in coalbearing formations.

200

KAOLIN MINERALS

In Japan, there are three major coal-fields, Ishikari in Hokkaido, Joban in northeastern Honshu, and Chikuho, etc. in northern Kyushu. In all, the coal seams are intercalated into the lower part of Paleogene sediments, mainly of the Eocene in Ishikari and Chikuho and the Oligocene in Joban. Mineralogical studies by Kobayashi and Oinuma (1960/61, 1963) and Oinuma and Kobayashi (1966) in Ishikari, and by Mukaiyama et al. (1964) in Chikuho, have shown that the lowermost part of the Eocene sediments in both areas is rich in kaolinite. Kaolinitic fireclays associated with coal in Ishikari, Joban and Chikuho have been described by Takayasu (1953), by Nagasawa et ul. (1969), and by Kodama et al. (1963) and Hoshino and Oishi (1965), respectively. They consist mainly of disordered kaolinite. Minor coal-fields also occur in the Kitakami mountainlands of northeastern Honshu. The Iwate clay mine in one of them is one of the most important refractory clay mines in Japan, and has been studied by Fujii (1970, 1972) and Iijima (1972b). Here, coal-bearing Oligocene sediments overlie the Cretaceous which contains the above-mentioned redbed at its top. Near the base of the Oligocene sediments, there is a bed of flint clay which consists of a compact aggregate of kaolinite sometimes associated with gibbsite. In the lower part of the Oligocene sediments, there are two coal seams each of which is associated with fireclay composed of kaolinite and quartz. These kaolinites are of the disordered type and have the shape of irregular plates. Many sedimentary kaolin deposits of Pliocene age are distributed around Nagoya, and constitute the most productive kaolin-mining area in Japan. Among them, the following are important: the Set0 area (Tanemura, 1963; Shimizu, 1972a) and Sanage-Fujioka area, Aichi Prefecture; the Tajimi-Toki area (Fujii, 1968), Hara area (Nagasawa and Tsuzuki, 1976) and Naegi area (Nagasawa and Kunieda, 1970), Gifu Prefecture; and Shimagahara area, Mie Prefecture. The lowermost part of the Pliocene formations in these areas is composed of lacustrine sediments deposited in many small-scale basins on a basement of granite, Paleozoic rocks, Miocene rocks, etc. The lower part of the lacustrine sediments is composed mainly of quartz sand and “Gaerome” clay, whereas the upper part is composed of “Kibushi” clay and silty clay. Lignite seams and carbonized wood fragments sometimes occur in the upper part. The Gaerome clay is a plastic kaolin clay including coarse quartz grains and occasional feldspar grains. The Kibushi clay is a dark-colored plastic kaolin clay stained by organic substances, and thus resembles the ball clay in England and the United States. The clay fraction of the Gaerome clay has almost the same mineral composition as the Kibushi clay: they are composed mainly of platy disordered kaolinite associated with minor amounts of tubular halloysite and quartz and with occasional illite and smectite. These sediments are considered to have been derived from the weathered rocks of nearby areas and to have been deposited after sorting.

KAOLINITE AND HALLOYSITE

201

5.2.3. Occurrence :post-depositional alteration of pyroclastics The weathering of volcanic ash and pumice to allophane and halloysite has been described in Chapter 2. White clay composed mainly of halloysite is known to have been formed frequently in the deeper portions of pyroclastic deposits by the action of ground water. The deposits at Ina and Yame are examples. Water-laid deposits of volcanic ash or pumice may also be altered to clay. Tazaki (1973) examined the ash-fall deposits beneath Nakaumi, a brackish lake in western Honshu, and showed that they are composed mainly of a 7 A kaolin mineral, illite, and halloysite. She considered the illite to be an alteration product of the vermiculite-chlorite intergrades which are abundant in the corresponding deposits on land. Uno and Takeshi (1971) examined vitric tuffs intercalated in partly freshwater and partly marine Plio-Pleistocene sediments to the south of Osaka, and found that they were weakly altered to smectite. Diagenetic alteration of Miocene tuffs to smectite associated with cristobalite and zeolite has also been described at many localities, but this subject lies beyond the immediate scope of the present Chapter. The author’s group (Nagasawa and Karube, 1975) has studied the mineralogy of clays formed by alteration of a bed of transported pumice intercalated in Pliocene freshwater sediments around Nagoya, and concluded that two kinds of alteration are involved. The first is early diagenetic alteration, by which smectite was formed in some places and kaolin minerals in others. The kaolin minerals thus formed are a mixture of kaolinite and halloysite. The second process was weathering after the sediments were upheaved. This is considered to be due to circulating ground water, and halloysite was formed by it (Nagasawa and Tsuzuki, 1976). Kaolin clays formed by alteration of pumice or tuff beds are known to be intercalated with the Pliocene sedimentary kaolin deposits around Nagoya mentioned above. The Shimmei kaolin in the Tajimi-Toki area (Fujii, 1968) and white clay in the Naegi area (Nagasawa and Kunieda, 1970) (Fig. 5.14) are examples. They are composed of kaolinite and halloysite or of halloysite alone. Vermicular kaolinite macrocrystals have been found in one of the white clay beds in the Naegi area. Nagasawa and Kunieda (1970) considered them to be an alteration product of biotite phenocrysts in the pumice. At the Iwate clay mine, a thin but continuous layer of grey clay composed of kaolinite occurs in a fireclay bed. It is considered to be an alteration product of pyroclastic material (Fuji, 1970)and may correspond to the “tonstein” of Europe. 5.2.4. Chemical composition

Chemical analysis data for kaolinite and halloysite are given in Tables 5.3 and 5.4, respectively. The modes of occurrence of the analyzed samples were as follows: Mikawa mine, a veinlet in a hydrothermal Cu-Pb-Zn vein; Niida, altered tuff around a Kuroko-type anhydrite deposit; Naegi, vermicular macro-

202

KAOLIN MINERALS

TABLE 5.3 Chemical analysis data of kaolinite Si02 Ti02 A1203 Fez03 FeO MnO MgO CaO NazO KzO HzO HzO Total SiOziAIz03

+

Mikawa 45.80 39.55 0.57 0.18 0.14 0.41 0.03 13.92 0.17 100.77 1.97

Niida

Naegi

43.58 0.49 38.82 0.43 tr.

42.68 0.18 35.64 3.20 0.26 0.02 0.14 0.15 0.24 0.21 13.65 4.32 100.70 2.03

0.43 0.25 0.29 0.26 14.34 0.98 99.87 1.90

Mikawa: Mikawa mine, Niigata Prefecture (Nagasawa, 1953). Niida: Drill core, Niida, Odate, Akita Prefecture (Kimbara and Nagata, 1974). Naegi : Kyoritsu-Naegi mine, Nakatsugawa, Gifu Prefecture (Yamada et al., 1949).

TABLE 5.4 Chemical ana!ysis data of halloysite SiOz Ti02 A1203

Fez03 FeO MnO MgO CaO NazO KeO HzO HaO-

+

Iki 38.15 0.05 35.40 2.15 0.05 tr. 0.75 tr. 0.40 0.11 13.42 10.18

P205

SrO Total SiOz/Alz03

100.61 1.83

Iwano 38.14 0.131 34.27 0.92 0.03 0.031 0.081 0.15 0.22 0.19 125.69 0.059 0.001 99.913 1.89

Iki: Iki mine, Iki Island, Nagasaki-Prefecture (Minato, 1969). Iwano: Iwano. Karatsu, Saga Prefecture (Ishibashi, 1974). Shichinohc: Shichinohe, Aomori Prefecture (Sud6 et al., 1951).

Shichinohe 39.58 30.24 1.74

tr. 0.98

11.08 16.60

100.22 2.22

KAOLINITE AND HALLOYSITE

203

crystals in an altered pumice in a Pliocene sedimentary kaolin deposit; Iki mine, hydrothermally altered vitric tuff; Iwano, an amygdale in basalt; and Shichinohe, Pleistocene bedded clay possibly originating from tuff. 5.2.5.

X-ray and electron diflraction

X-ray diffraction diagrams for selected samples of kaolinite and halloysite are shown in Fig. 5.7. As noted by Iwai (1955), there is a wide variation in the structural integrity of Japanese kaolinite. The most ordered variety, triclinic kaolinite with split (111) and (111) reflections, has been reported from the Roseki deposits at the Kurata mine, Yamaguchi Prefecture (Sudo et al., 1954); the Kawaguchi mine, Akita Prefecture (Honda and Shiikawa, 1957); the Roseki deposits at the Goto mine, Goto Islands, Nagasaki Prefecture (Takeshi, 1958); the Mikawa mine, Niigata Prefecture (Nagasawa, 1961); the Akatani iion mine, Niigata Prefecture (Imai et al., 1965); and the Toseki deposits in the Amakusa Islands, Kumamoto Prefecture (Ozaki et al., 1975). Hydrothermal kaolinites are usually ordered, as exemplified by those at the Kampaku mine and Ibusuki (Iwai, 1955), the Hiraki mine (Tanaka et al., 1963), and the Ebara mine (Ueno, 1964), although the (1 1I) and (11I) reflections are not split in them. More disordered varieties have been reported from the Konomai mine (Sudo, 1954b) and the Roseki deposits at Namera and Tsubonouchi, Yamaguchi Prefecture (Takeshi, 1958). At the Mikawa mine, the kaolinite in the altered wall rocks tends to be more disordered than that in the veins (Nagasawa, 1961). At the Seta mine, the kaolinite in the kaolin zone is more disordered than that in the surrounding quartz-kaolin-alunite zone (Komura and Sudo, 1976). Sedimentary kaolinites are of disordered type irrespective of age. Shimizu (1972b) compared the Hinckley crystallinity index of kaolinites from Pliocene sedimentary deposits around Nagoya with that of kaolinites from Oligocene sedimentary deposits at the Twate clay mine. His results indicated that the former falls mostly between 0.0 and 0.6, whereas the latter falls between 0.3 and 0.8. As shown in Fig. 5.7, kaolinite macrocrystals pseudomorphous after biotite are more ordered than ordinary sedimentary kaolinite. Iwai and Kuroda (1961) examined the X-ray diagrams of sedimentary kaolins from around Nagoya, and showed that the basal spacing is 7.14-7.23 and the mean thickness of the crystallites 150-250 A. The latter value is much smaller than that for ordered hydrothermal kaolinite, several hundred A or more (Iwai, 1959; Iizuka and Kobayashi, 1975). Halloysite has a disordered structure characterized by two-dimensional (I&) bands in X-ray diffraction diagrams (Fig. 5.7). Honjo et al. (1954) examined tubular halloysite samples from Hong Kong and other areas outside Japan, by selected-area electron diffraction as well as X-ray diffraction, and revealed that they have a stacking sequence with two-layer periodicity. Later, such two-layer stacking was also found to be valid for tubular halloysites in Japan, viz. halloysites from the Takatama gold mine (Kitamura, 1958), from weathered granite

A

28

(c~K~)

Fig. 5.7. X-ray diffraction diagrams of kaolinite and halloysite (air-dried and unoriented). A, Kaolinite from the Mikawa mine, Niigata Prefecture, hydrothermal; B, kaolinite from the Kyoritsu-Naegi mine, Nakatsugawa, Gifu Prefecture, altered biotite in a pumice bed; C, kaolinite from the Sone mine, Hara, Gifu Prefecture, clay fraction of Gaerorne clay; D, halloysite from Noma, Aichi Prefecture, matrix of sand in the Pleistocene Noma Formation; E, halloysite from Misuzu, Ina, Nagano Prefecture, deep-weathered pumice. Q denotes quartz reflection.

KAOLINITE AND HALLOYSITE

205

at Kakino (Shimizu, 1972a), from weathered granite and sand matrix at various localities (Nagasawa and Miyazaki, 1976), and from Kusatsu (Kohyama et al., 1977). The study by Kohyama et nl. is particularly important since it demonstrated that halloysite has two-layer stacking in the hydrated state. The cell parameters determined by them for the hydrated material are a = 5.14, b = 8.90, c = 20.7 A, p = 99.7'. An example of the selected-area electron diffraction patterns obtained by the present author is given in Fig. 5.8.

Fig. 5.8. Selected-area electron diffraction photograph of halloysite from Morowa, Aichi Prefecture. The scale-line in the accompanying electron micrograph represents 1 ,urn.

Nagasawa (1969) reported variations in the stability of the interlayer water and in the b-dimension of halloysite, the latter arising from the former at least in part. Nagasawa and Miyazaki (1976) examined many halloysite samples of various origins and showed that all were in a fully hydrated state when half-dried at 100% r.h. ; however, the degree of hydration differed from sample to sample when drying was carried out at 56 % r.h. (Fig. 5.9). They further suggested that the stability of the interlayer water may be related to the age of formation of the halloysite; that is, older halloysite tends to have less stable interlayer water. Iwai (1959) showed from line broadening of the (002) reflection that crystallites of three halloysite samples had a thickness of 50-90 A, while Watanabe (1975) showed by analysis of the line profiles of (001) reflections that crystallites of two halloysites from the Shimosueyoshi Loam had a thickness of 30-50 A.

KAOLIN MINERALS

206

D

I

I

6

I

10

I

I

I

14

6

I

I

10

I

I

I

14

6

I

I

10

I

I

14

6

10

14

2 '6 (CuKu)

Fig. 5.9. X-ray diffraction diagrams of halloysite half-dried at 100% r.h. (upper) and dried at 56% r.h. (lower); oriented aggregate. A, Noma, Aichi Prefecture; B, Otaki, Nagano Prefecture; C, Okusa, Komaki, Aichi Prefecture; D, Misuzu, h a , Nagano Prefecture.

5.2.6.

Inpared absorption

Examples of infrared spectra for kaolinite and halloysite are given in Fig. 5.10. The two minerals exhibit similar spectra except that, as noted by Beutelspacher and van der Mare1 (1961) and by Oinuma and Kodama (1964), halloysite shows broader absorptions and does not have the 940 cm-l band. Nagasawa and Miyazaki (1976) demonstrated that the absorbance ratio of the two OHstretching vibration bands, A3700/A3620, is variable (Fig. 5.1 l), and that older halloysite tends to have a larger value for this ratio. They ascribed the larger values to high structural integrity. Kodama and Oinuma (1963) showed that halloysite has an absorption band at 3570 cm-l. Kato (1976), as a result of extensive studies on the infrared spectra of kaolin minerals, concluded that this small absorption (at 3550 cm-l according to him) was characteristic of halloysite. Farmer (1974) considered the absorption to be due to the hydrogen-bonded hydroxyl, and Yariv and Shoval (1975) assigned this to water in the interlayer space. According to the present author's data (Nagasawa and Miyazaki, M published), this band appeared in the spectra of most of halloysites examined and became weak on drying of the samples at 110°C for 2 hr.

KAOLINITE AND HALLOYSITE

207 x102

Fi

.

5.10. Infrared absorption spectra of kaolinite and halloysite. The samples and labeling are asln Fig. 5.7.

Fig. 5.1 1. OH-stretching bands in infrared spectra of halloysite. The samples and labeling are as in Fig. 5.9.

208

KAOLIN MINERALS

5.2.7. Morphology

Kaolinite always has a platy shape with a tendency to show a hexagonal outline. Some halloysites, e.g. that from the Joshin mine, exhibit tubular morphology. However, some other halloysites have spherical shapes, as established by Sudo (1951, 1953) and Sudo and Takahashi (1956). Detailed geological descriptions of most of their samples of spherical halloysite are not available, although they have indicated that these halloysites were alteration products from vitric tuff. The samples consist of rounded grains, sometimes with polygonal outlines and/ or concentric cracks, and elongated crystals often project out from the rounded grains. Examples of spherical halloysite have been reported from weathered volcanic ash and pumice by Nozawa (1953), Morimoto et al. (1957), Kurabayashi and Tsuchiya (1960), Matsui (1960), Ishii and Kondo (1963), etc., as well as by Sudo (1954a, 1956) himself. They are described in Chapter 2. The white clay in the deeper parts of the Quaternary pyroclastics described in Chapter 2 consists of spherical halloysite, as exemplified by the Yame clay (Kinoshita and Muchi, 1954; Sudo and Takahashi, 1956)and the Ina clay (Nagasawa et al., 1969).Spherical halloysite has also been described from altered pumice beds in the Pliocene sedimentary kaolin deposits at Naegi (Nagasawa and Kunieda, 1970) and the hydrothermal deposits at the Iki mine (Nagasawa et al., 1969; Minato and Utada, 1969). Nagasawa and Miyazaki (1976) have shown that the morphology of halloysite is closely related to its genesis. Halloysites formed by alteration of pyroclastics have the shape of balls or scrolls, sometimes associated with short tubes, whereas those formed by weathering of feldspar in granitic rocks and those formed by deep weathering of sands have the shape of long tubes (Fig. 5.12). Hydrothermal halloysites exhibit both types of morphology. Nagasawa and Miyazaki (1976) ascribed this difference in morphology to the mode of formation; that is, replacement for the former and crystallization in free space for the latter. 5.2.8. Distinction between kaolinite and halloysite

Chukhrov and Zvyagin (1966) established halloysite as a distinct mineral species from kaolinite. As shown by Honjo et al. (1954), it has a stacking sequence with a two-layer periodicity in contrast to the one layer of kaolinite. All the halloysites for which two-layer periodicity was established by electron diffraction so far exhibit the long tubular form. Electron diffraction studies of spherical, scroll-shaped, and short tubular halloysites are thus required. As shown by Chukhrov and Zvyagin (1966), the X-ray pattern in the range of 28 = 20-25" (CuKa) is diagnostic, although halloysite does not usually exhibit distinct reflections in this region due to its stacking disorder. Nagasawa and

GENESIS

209

Fig. 5.12. Electron micrographs of halloysite. A, Iki mine, Iki Island, Nagasaki Prefecture, hydrothermal; B, Misuzu, Ina, Nagano Prefecture, deep-weathered pumice; C, Yamaka mine, Nakatsugawa, Gifu Prefecture, altered pumice; D, Okusa, Komaki, Aichi Prefecture, deep-weathered pumice. The scale-lines represent 0.5 pin.

210

KAOLIN MINERALS

Fig. 5.12 (continued). Electron micrographs of halloysite. E, Morowa, Aichi Prefecture, deep-weathcrcd sand matrix; F, Naegi-Kogyo mine, Nakatsugawa, Gifu Prefecture, weathered feldspar in granite. The scale-lines represent 0.5 ,urn.

Miyazaki (1976) concluded that some of their samples of altered pyroclastics and weathered granite are composed of both kaolinite and halloysite on the basis of the presence of two basal reflections, 7 A and 10 A, for materials halfdried at 100% r.h., the presence of weak reflections characteristic of kaolinite in the range of 20 = 20-25" (CuKa), and the presence of platy crystals together with balls, scrolls or long tubes (Fig. 5.13). These three criteria yielded consistent results; that is, samples with the 7 A basal reflection showed kaolinite lines in the range of 20 = 20-25" and contained platy particles. The most convenient method for distinguishing these two minerals may thus be to examine the basal reflection on X-ray diagrams for materials half-dried at 100% r.h., since this is the most sensitive. However, it is possible that the above concordance in results could arise simply from the limited coverage of the samples. In this connection, Brindley and Souza Santos (1966) have reported that some samples show a discordance between morphology and X-ray properties. Sudo et al. (1950) reported that a kaolin mineral from the Zao sulfur mine had an X-ray pattern characteristic of kaolinite but exhibited tubular morphology. Tsuchiya and Kurabayashi (1958) and Kurabayashi and Tsuchiya (1960) described a kaolin mineral with a diffuse basal reflection between 7 and 10 A and a platy morphology with coexistent tubes, in pyroclastic deposits around Tokyo. The basal reflection of their samples was not composed of separate 7 A and 10 A peaks, but consisted of a continuous diffuse reflection ranging from 7 8, to 10 A which, as shown by

3ENESIS

6

10

14

2 8 (GuKa)

Fig. 5.1 3. Electron micrographs and X-ray diffraction diagrams of halloysite associated with kaolinite. The X-ray diagrams were recorded for oriented aggregates half-dried at 100% r.h. Thescalelines in the electron micrographs represent 0.5 pm. A, Naegi-Kogyo mine, Nakatsugawa, Gifu Prefecture, altered pumice; B, Yamaman-Shimmei mine, Toki, Gifu Prefecture, altered tuff; C, KyoritsuNaegi mine, Nakatsugawa, Gifu Prefecture, weathered feldspar in granite.

KAOLIN MINERALS

212

Churchman et al. (1972), may be due to interstratifications of 10 A halloysite and 7 A dehydrated halloysite. In these examples, the X-ray properties appeared to be inconsistent with the morphology, and further investigations on such materials are thus necessary. Infrared absorption and thermal analysis may constitute useful methods for distinguishing between kaolinite and halloysite. As mentioned above, most, although not all, halloysites exhibit the 3550 cm-1 band in infrared spectra. Minato (1965b) has shown that the dehydroxylation temperature on thermogravimetric curves recorded under near-equilibrium conditions is different for kaolinite and halloysite. The slope ratio of the dehydroxylation peak on differential thermal curves has been proposed as a criterion for differentiating between kaolinite and halloysite (Bramao et al., 1952), although the present author’s results for sedimentary kaolin minerals in central Japan indicate that this may not always be so (Nagasawa, 1969). 5.3,

GENESIS

5.3.1. Hydi8otheruMal

Hemley and Jones (1964) classified the mineral assemblages of hydrothermally altered rocks into three types, viz. incipient associations, intermediate associations, and advanced associations, according to the intensity of hydrogen metasomatisni. Although Nagasawa (1961) reported the occurrence of kaolinite as a product of alteration of an intermediate association from the outer envelope of ore veins at the Mikawa mine, the important occurrences of kaolin minerals belong to advanced associations. Kaolin minerals of such associations result from the action of acid hydrothermal solutions which have leachcd out bases from the rocks. As indicated by Iv(iao (1952, 1958, 1968), the most important feature of the hydrothermal kaolin deposits and other kaolin-bearing deposits, e.g. Roseki deposits, silica-alunite deposits and sulfur deposits, is the zonal arrangement of different minerals. Some of these deposits, e.g. the Roseki deposits at the Goto mine, were formed at the relatively high temperatures which accompany igneous intrusions. Some others, e.g. the sulfur deposits, were farmed under shallow volcanic conditions. In spite of this difference in formational conditions, however, zonal distribution of minerals is a common feature of the deposits. In the Roseki deposits of the Goto mine, a diaspore-rich central zone is surrounded by a pyrophyllite-quartz zone, i.e. they have an alumina-rich core (Iwao et al., 1953;Minato and Kato, 1963). Many other Roseki deposits exhibit similar zonal sequences (Takeshi, 1958; Kinosaki, 1963, 1965; Minato, 1965a; Fujii and Inoue, 1971). One example from the Shokozan area is shown above in Fig. 5.1. As seen from the figure, the zonal arrangement in this area is not so regular,

GENESIS

213

a fact which may be explained by formation conditions in which the rising hydrothermal solutions were locally mixed with meteoric water (Katayama, 1969). Differences in oxidation state between the hanging-wall side and the footwall side support this hypothesis. Kinosaki (1965) noted that the zoning in the Fukuyama deposit does not conform with that in other Roseki deposits. Also, Fujii and Inoue (1971), after reviewing the Roseki deposits of the Hokushin district, Nagano Prefecture, concluded that the Bontenyama deposit exhibits reverse zoning, i.e. silicification zone (center)+pyrophyllite zone-weakly altered zone (margin). The zonal sequences of silica-alunite deposits, e.g. Ugusu and Beppu, and volcanic sulfur deposits are similar to that at Bontenyama, i.e. with a central zone of silicification. Examples are shown above in Figs. 5.2. and 5.5. The alteration zones of active geothermal areas are essentially similar to them (Sumi, 1969; Hayashi, 1973). Two kinds of zonation thus exist, one with an alumina-rich core and the other with a silica-rich core. Minato and Kato (1961) undertook alteration experiments by placing rocks in the hot springs of Beppu and Tamagawa. Alteration to opal and halloysite occurred in the Beppu hot spring at a pH of about 3, but alteration only to opal occurred in the Tamagawa hot spring at a pH of 1.0-1.2. A strongly acid solution seems to favor the formation of silica, since the solubility of alumina under such conditions is high. Tsuzuki (1976) constructed solubility diagrams for the A1z03-Si02-Hz0 system, and, based on the diagrams, explained the two kinds of zonal sequences in terms of the difference in acidity of the solutions. A weakly acid solution becomes saturated first with respect to aluminum minerals, since the solubility of these minerals is low. A strongly acid solution, on the other hand, becomes saturated first with respect to silica, since the solubility of aluminum minerals is much higher in it. Consequently, alteration zoning with a silica-rich core is attributed to a strongly acid solution, whereas that with an alumina-rich core is attributed to a weakly acid solution. Differences in the conditions of formation of nacrite, dickite, kaolinite, and halloysite represent an important problem. Nacrite and dickite tend to be formed as fillings in veins or interstices, i.e. by precipitation from solution. When these minerals occur in the altered rocks themselves, dickite tends to be located in the inner part of the kaolin zone, as seen at the Ugusu mine (Uno and Takeshi, 1977), Kasuga mine (Tokunaga, 1954, 1955) and Akatani iron mine (Tmai, 1960), while halloysite tends to be located in the outer part of the kaolin zone, as seen in the Zao sulfur mine (Mukaiyama, 1959). 5.3.2.

Weathering and sedimentary

Three factors appear to control the differential formation of kaolinite and halloysite in weathered rocks. As mentioned above, kaolinjte is abundant in surface soils, whereas halloysite occurs in the saprolites of deeper horizons. The

KAOLIN MINERALS

214

Coarse sand

Altered pumice

5

10

15

28 ( c ~ K ~ )

Fig. 5.14. Columnar sections of the lower part of the sedimentary kaolin deposits at the Yamaka mine, Nakatsugawa, Gifu Prefecture, and X-ray diffraction diagrams of samples taken from this locality, half-dried at 100% r.h.

REFERENCES

21 5

reason for this contrasting mineralogy remains unknown, although it should be noted that the halloysite, and also that occurring in hydrothermally altered rocks and altered pyroclastics, is not usually accompanied by any other clay mineral. The second controlling factor is the original mineral. As pointed out by Sand (1956), feldspars are weathered to halloysite, whereas biotite is weathered to kaolinite. Examples have been given by Shimizu (1972b), and kaolinite macrocrystals pseudomorphous after biotite, have been reported from several localities (Mitsuda, 1960b; Tsuzuki et al., 1968; Nagasawa and Kunieda, 1970; Tazaki and Tazaki, 1975). The third factor is age. The clay fraction of saprolites of present-day weathering belts is composed almost exclusively of halloysite (Shimizu, 1972b). Weathered feldspar in basement granite covered by Pliocene sediments is composed of halloysite and kaolinite, as shown in Fig. 5.6. At the Iwate clay mine, halloysite does not occur in the weathered rocks covered by Oligocene sediments. These facts support the suggestion of Parham (1969a, b) that halloysite is converted to kaolinite with age. Nagasawa and Miyazaki (1976) have also arrived at a similar conclusion based on mineralogical studies of halloysite of various origins. The difference in mineral composition between Pliocene sedimentary kaolin and the underlying weathered granite represents another important problem. As mentioned above, the Pliocene sedimentary kaolin deposits around Nagoya are composed mainly of kaolinite associated with small amounts of halloysite. The basement granite, on the other hand, is composed of halloysite and kaolinite, the relative amounts being variable. As a whole, the weathered granite contains more halloysite than the overlying clays. One example is given in Fig. 5.14. The halloysite in the weathered granite is of tubular shape and much longer and thicker than that in the overlying clays. Nagasawa and Kunieda (1970) considered that transformation of halloysite to kaolinite has occurred during transportation and early diagenesis. The gradual increase in halloysite observed in sediments from the bottom upwards appears to support this view. Shimizu (1972b), however, has given an alternative explanation for the differences in kaolin minerals based on the fact that the surface layer of the present-day wealhering belt is rich in kaolinite, in contrast to the halloysite-rich nature of deeper horizons. He considers that the kaolinite in the surface layer of the Pliocene weathering belt was eroded out to become one component of the Pliocene sediments, leaving the latter richer in kaolinite than the deeper parts of the Pliocene weathering belt which now remains as basement. The present author suspects that both these mechanisms may have operated. REFERENCES Ando, T. (1952) Geol. Suuv. Japan Rept. NO. 141. Aoki, S., Oinuma, K. and Kobayashi, K. (1975) Contributions to CIay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 161.

216

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Aomine, S. (1969) The Clays of Japan, Geol. Surv. Japan, 167 Aoyagi, K., Kobayashi, N. and Kazama, T. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 167. Aoyagi, K., Kobayashi, N. and Kazama, T. (1976) Proc. Intern. Clay Conf. Mexico City 1975, 101. Bates, T. F. (1952) Problems of Clay and Laterite Genesis, p. 144, Amer. Inst. Mining Metall. Eng. Beutelspacher, H. and van der Marel, H. W. (1961) Tonindustr.-Zeitung 85, 517, 570. Bramao, L., Cady, J. G., Hendricks, S. B. and Swerdlow, M. (1952) Soil Sci. 73, 273. Brindley, G. W, and Souza Santos, P. de (1966) Proc. Intern. Clay Conf. Jerusalem 1966,1,3. Chukhrov, F. V. and Zvyagin, B. B. (1966) Proc. Intern. Clay Conf. Jerusalem 1966,1, 11. Churchman, G. J., Aldridge, L. P. and Carr, R. M. (1972) Clays Clay Miner. 20, 241. Farmer, V. C. (1974) The Infrared Spectra of Minerals (ed. V . C. Farmer), p. 331, Mineralogical Society. Fujii, N. (1961) Bull. Geol. Surv. J a p n 12, 647. Fujii, N. (1962) Bull. Geol. Surv. Japan 13, 231. Fujii, N. (1968) Ceol. Surv. Japan Rept. No. 230. Fujii, N. (1970) J. Geol. SOC.Japan 76, 623. Fujii, N. and Inoue, H. (1971) Mining Geol. 21, 407. Fujii, N. and Yasuda, T. (1971) Bull. Geol. Surv. Japan 22, 593. Fujii, N. (1972) Kaolin Symposium, 1972 Intern. Clay Conf., 17. Fujii, N. (1976) The 7th Symposium on Genesis of Kaolin, 1. Fujiwara, T. and Kujirai, S. (1972) Mining Geol. 22, 213. Hayashi, H. (1961) J . Miner. Soc. Japan 5 , 101. Hayashi, M. (1973) J. Japan Geotherm. Energy Assoc. 10, (3), 9. Hemley, J. J. and Jones, W. R. (1964) Econ. Geol. 58, 538. Honda, S. and Shiikawa, M. (1957) Rept. Inst. Develop. Underground Resources Akiia Univ. 18,l. Honda, S., Hayashi, A. and Shimazaki, K. (1963) Industrid Mineral Resources in the Tohoku District, vol. 3, p. 76. Honda, S., Miura, T., Ohira, Y . and Tamanoi, M. (1964) Industrial Mineral Resources in the Tokoku District, vol. 4, p. 87. Honjo, G., Kitamura, N. and Mihama, K . (1954) Clay Miner. Bull. 2,133. Hoshino, Y. and Oishi, M. (1965) Advances in Clay Science, vol. 5, p. 241, Gihodo. Hukuo, K. and Kutina, S. (1960) Advances in Clay Science, vol. 2, p. 101, Gihodo. Ichiko, T. (1971) J. Clay Sci.SOC.Japan, 11, 1. Igo, H . (1961) J. Geol. SOC. Japan, 67, 261. Iijima, A. (1972a) Mining Geol. 22, 1 . Iijima, A. (1972b) J. Fac. Sci. Univ. Tokyo Sec. 11, 18, 325. Iizuka, M. and Kobayashi, K. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 23. Imai, N. (1960) J. Fac. Sci. Niigata Univ. Ser. II,3,205. Imai, N., Otsuka, R. and Watanabe, K . (1965) J. Clay Sci. SOC.Japan 4, 113. Ishibashi, K. (1974) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 69, 255. Ishii, J. and Kondo, Y . (1963) Advances in Clay Science, Vol. 4, p. 193, Gihodo. Isobe, K., Hoshina, K. and Sugaki, A. (1967) Mining Geol. 17, 22. Iwai, S., Takeshi, H. and Ossaka, J (1949) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 33, 169. Iwai, S. (1955) Miner. J. 1, 233. Iwai, S. (1959) Advances in Clay Science, vol. 1, p. 28, Gihodo. Iwai, S. and Kuroda, Y . (1961) Advances in Clay Science, vol. 3, p. 160, Gihodo. Iwamoto, S. (1963) Geof. Rept. Hiroshima Univ. 12, 73. Iwao, S. (1949) Geol. Surv. Japan Rept. No. 130. Iwao, S. (1952) Mining Geol. 2, 120. Iwao, S., Hamachi, T., Yamada, M. and Inoue, H . (1953) Bull. Geol. Surv. Japan 4, 81. Iwao, S. (1958), Sci. Pap. Coll. Gen. Educ. Univ. Tokyo 8, 93. Iwao, S. (1962) Japan. J. Geol. Geograph. 33, 131. Iwao, S. (1968) Proc. 23rd Intern. Geol. Congr. Prague, 14, 107. Iwao, S. (1970) Volcanism and Ore Genesis (ed. T. Tatsumi), p. 267, Univ. Tokyo Press. Kakitani, S. and Kono, T. (1972) J. Clay Sci. SOC. Japan 12, 51. Katayama, N. (1969) Mining Geol. 19, 31.

REFERENCES

217

Kato, E. (1976) D. Sc. Thesis, Tokyo Kyoiku Daigaku. Kato, Y . (1964/65) Soil Sci. Plant Nutr. (Tokyo) 10,258,264; 11, 30,62, 114, 123. Kitamura, N. (1958) Clays and Their Utilization (ed. T. Sueno and S. Iwano), p. 127, Asakura Shoten. Kimbara, K. and Nagata, €3. (1974) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 69, 239. Kimura, M. (1951) J. Geol. SOC.Japan 57, 499. Kinosaki, Y . (1963) Geol. Rept. Hiroshima Univ. 12, 1. Kinosaki, Y . (1965) J. Miner. SOC.Japan 7, 185. Kinoshita, K. and Muchi, M. (1954) J. Mining Znst. Kyushu 22, 279. Kinoshita, K. and Muta, K. (1953) Mining Geol. 3, 7. Kinoshita, K. and Muta, K. (1954) Mining Geol. 4, 79, Kobayashi, K. and Oinuma, K. (1960/61) J. Geol. SOC.Japan 66, 506; 67, 14. Kobayashi, K. and Oinuma, K. (1963) Advances in Clay Science, vol. 4, p. 117, Gihodo. Kobayashi, K. and Oinuma, K. (1965) Advances in Clay Science, vol. 5, p. 69, Gihodo. Kodama, H. (1963) Advances in Clay Science, vol. 4, p . 179, Gihodo. Kodarna, H. and Oinuma, K. (1963) Clays Clay Miner. 11, 236. Kodama, H., Hoshino, Y . and Furusato, I. (1963) Advances in Clay Science, vol. 4, p. 301, Gihodo. Kohyama, N., Fukushima, K. and Fukami, A. (1977) J. Miner. SOC.Japan 13, Spec. Issue, 17. Komura, T. and Sudo, T. (1976) Clay Sci. 5, 9. Kurabayashi, S. and Tsuchiya, T. (1960) J. Geol. Soc. Japan 66, 586. Matsui, T. (1959) Advances in Clay Science, vol. 1 , p. 244, Gihodo. Matsui, T. (1960) Advances in Clay Science, Vol. 2, p. 229, Gihodo. Matsukurna, T. and Tanaka, N. (1955) Tech. Rept. Kyushu Univ. 27, 183. Matsumoto, K. (1968) Geol. Rept. Hiroshima Univ. 16, 1. Minato, H. and Kato, T. (1961) Advances in Clay Science, vol. 3, p. 264, Gihodo. Minato, H. and Kato, T. (1963) Advances in Cloy Science, vol. 4, p. 95, Gihodo. Minato, H . (1965a) J. Miner. SOC.Japan 7, 200. Minato, H . (1965b) Advances in Clay Science, vol. 5, p. 169, Gihodo. Minato, H. and Utada, M. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 393. Minato, H. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 73. Minato, H. (1976) The 7th Symposium on the Genesis of Kaolin, 17. Mitsuda, T. (1960a) J. Miner. SOC.Japan, 4, 335. Mitsuda, T. (1960b) J. Fac. Sci. Hokkaido Univ. Ser. IV, 10,481. Morimoto, R., Ossaka, J. and Fukuda, T. (1957) Bull. Earthquake Res. Znst. 35, 359. Mukaiyama, H. (1959) J. Fac. Sci. Univ. Tokyo Sec. 11, 11, Supplement, 1. Mukaiyama, H., Miyagi, S., Arimitsu,T. and Mori, K . (1964) J. Mining Inst. Kyushu 32,139,235,401. Muraoka, M . (1951) Bull. Geol. Surv. Japan 2, 74. Muraoka, M. and Tanemura, M. (1954) Bull. Geol. Surv. Japan 5, 297. Muraoka, M., Iwao, S., Tanemura, M., Kinoshita, K., Tanaka, N. and Oono, M. (1958) CZays nnd Their Utilization (ed. T. Sueno and S. Iwao), p. 204, Asakura Shoten. Mutoh, T. (1952) Mining Geol. 2, 131. Nagasawa, K. (1953) J . Earth Sci. Nagoya Univ. 1,9. Nagasawa, K. (1961) J. Earth Sci. Nagoya Univ. 9, 129. Nagasawa, K. (1966) J. Clay Sci. SOC.Japan 6 , 3. Nagasawa, K. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 15. Nagasawa, K., Takeshi, H., Fuji, N. and Hachisuka, E. (1969) The Chys of Japan, Geol. Surv. Japan, 17. Nagasawa, K. and Kunieda, K. (1970) Mining Geol. 20, 361. Nagasawa, K. and Karube, K. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 180. Nagasawa, K. (1976) The 7th Symposium on the Genesis of Kaolin, 32. Nagasawa, K. and Miyazaki, S. (1976) Proc. Intern. Clay Conf. Mexico City 1975, 257, Nagasawa, K., Shirozu, H. and Nakamura, T. (1976) Mining Geol. Spec. Issue No. 7,75. Nagasawa, K. and Tsuzuki, Y. (1976) Geology of the Seto, Shokozan and Itaya Kaolin Deposits-A Guide to the Field Investigations The 7th Symposium on the Genesis of Kaolin, 1. Nakagawa, Z., Ossaka, J., Urabe, K. and Yarnada, H. (1972) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 67,283.

218

KAOLIN MINERALS

Nishiyama, T., Oinuma, K. and Ueda, F. (1973) J. Toyo Univ., Gen. Educ. (Nut. Sci.) 16, 21. Nozawa, K. (1953) Misc. Rept. Res. Znst. Nut. Resources 30, 56. Oinuma, K. and Kobayashi, K. (1963) Advances in Clay Science, vol. 4, p. 109, Gihodo. Oinuma, K. and Kodama, H. (1964) J. Toyo Univ., Gen. Educ. (Nut. Sci.) 5 , 1. Oinuma, K. and Kobayashi, K. (1966) Clays Clay Miner. 14, 209. Oinuma, K. and Hayashi, H. (1968) J. Toyo Univ. Gen. Educ. (Nut. Sci.) 9, 57. Oinuma, K. (1969) The Clays ofJapan, p . 149, Geol. Surv. Japan. Ozaki, M., Watanabe, T. and Fukunari, C. (1975) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 70,33. Parham, W. E. (1969a) Clays Clay Miner. 17, 13. Parham, W. E. (1969b) Proc. Intern. Clay Conf. Tokyo 1969,1,403. Sand, L. B. (1956) Amer. Miner. 41,28. Shikazono, N. (1975) Econ. Geol. 70, 694. Shimizu, H. (1971) M. Sc. Thesis, Nagoya Univ. Shimizu, H. (1972a) J. Clay Sci. SOC.Japan 12, 11. Shimizu, H. (1972b) J. Clay Sci. SOC.Japan 12,63. Shirozu, H., Date, T. and Higashi, S. (1972) Mining Geol. 22, 393. Sudo, T., Kawashima, C. and Tazaki, H. (1950) J. Ceram. Assoc. Japan 58, 6. Sudo, T. (1951) Science 113, 266. Sudo, T., Minato, H and Nagasawa, K. (1951) J. Geol. SOC.Japan 57,473. Sudo, T. (1953) Miner. J. 1, 66. Sudo, T. (1954b) Sci. Rept. Tokyo Kyoiku Daigaku Sec. C , 3, 173. Sudo, T., Takahashi, H. and Matsui, H. (1954) Japan. J. Geol. Geograph. 24,71. Sudo, T. (1954a) Clay Miner. Bull. 2, 96. Sudo, T. (1956) Sci. Rept. Tokyo Kyoiku Daigaku Sec. C , 5 , 39 Sudo, T. and Takahashi, H. (1956) Clays Clay Miner. 4, 67. Sudo, T. and Hayashi, H. (1957) Miner. J. 2, 187. Sudo, T., Hayashi, H. and Yokokura, H. (1958) Clay Miner. Bull. 3, 258. Sugiura, S. and Nakano, H. (1960) Advances in C1a.v Science, vol. 2, p . 107, Gihodo. Sumi, K. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 501. Takayasu, M. (1953) J. Miner. SOC.Japan 1, 78. Takeshi, H. (1958) J. Miner. SOC.Japan 3, 388. Takeuchi, T., Takahashi, I. and Abe, H. (1966) Sci. Repi. Tohoku Univ. Ser. 111,9, 381. Takubo, J., Ukai, Y. and Yokoi, T. (1954) Mining Geol. 4, 94. Tanaka, M., Taninami, S. and Oya, I. (1963) J. Ceram. Assoc. Japan 71, 187. Tanemura, M. (1954) Bull. Geol. Surv. Japan 5,647. Tanemura, M. and Horiuchi, H. (1958) Bull. Geol. Surv. Japan 9, 247. Tanemura, M. (1963) Geol. Surv. Japan Rept. No. 203. Tazaki, K. (1973) J. Geol. SOC.Japan 79, 79. Tazaki, K. and Tazaki, K. (1975) Contributionsto Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 145. Togashi, Y . and Fujii, N. (1972) Bull. Geol. Surv. Japan 23, 595. Togashi, Y. (1974) Bull. Geol. Surv. J q a n 25, 491. Togashi, Y. (1976) Geology of the Seto, Shokozan and Ztaya Kaolin Deposits-A Guide to the Field Investigations The 7th Symposium on the Genesis of Kaolin, 16. Tokunaga, M. (1954) Mining Geol. 4, 205. Tokunaga, M. (1955) Mining Geol. 5 , 1. Tokunaga, M. (1957) Miner. J. 2, 103. Tsuchiya, T. and Kurabayashi, S. (1958) J . Geoi. SOC.Japan 64,605. Tsuzuki, Y., Nagasawa, K. and Isobe, K. (196s) Miner. J. 5 , 365. Tsuzuki, Y. (1976) Clays Clay Miner. 24, 297. Ueno, M., Tsukawaki, Y . ,Takahashi, H. and Iwao, S. (1958) Bull. Geol. Surv. Japan 9,263. Ueno, M. (1964) Bu!~.Ceol. Surv. Japan 15, 235. Uno, Y. and Takeshi, H. (1971) J. Clay Sci. SOC.Japan 11, 25. Uno, Y. and Takeshi, H. (1977) J. Miner. SOC.Japan 13, Spec. Issue, 207. Urashima, Y. (1953) Mining Geol. 3, 174. Urashima, Y. and Sato, J. (1967) J. Mining Znst. Hokkaido 23, 171.

REFERENCS

219

Watanabe, T. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sndo on the Occasion of His Retirement, 18. Watanabe, Y., Kitagawa, Y. and Sugo, S. (1969) Proc. Intern. Clay Conf. Tokyo 1969,1,129. Yajima, S., Tsutsumi, S. and Suzaki, Y. (1970) Sci. Res. School Educ. Wusedu Univ. Ser. Biol. Geol., 19, 59. Yamada, H., Iwai, S. and Hata, T. (1949) Ceramic Raw Materials, vol. 2, p. 191, Gakujutsu-Tosho. Yamamoto, T. (1959) J. Miner. SOC.Japan 4, 277. Yamamoto, T. (1965) J. Miner. SOC.Jupan 7 , 209. Yariv, S. and Shoval, S. (1975) Cluys Clay Miner. 23,473. Yoshiki,B. (1934) J. Japan. Assoc. Miaer. Petrol. Econ. Geol. 12, 107, 165.

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Chapter 6 Smectites

Hideo TAKESHI

The term smectite can be used as a group name for all clay minerals with an expanding lattice except vermiculite, and montmorillonite is a specific mineral name of the smectite group. Although in Japan several species of smectite such as montmorillonite, saponite, nontronite, stevensite, etc. occur and have been studied by many workers, only montmorillonite forms clay deposits of economic importance. The mineralogy of montmorillonite and the geology and geochemistry of montmorillonite deposits have therefore been investigated in detail. Montmorillonite deposits of economic importance are distributed only in Tertiary formations, especially in the Green Tuff regions of Miocene age. Iron-rich saponites occur widely as alteration products of volcanic ash and rocks of medium/basic composition in the Tertiary, especially in the Green Tuff regions of Miocene age. Nontronite is also found as an alteration product of basalt. Stevensite is known from a lead-zinc deposit formed by alteration of a calcareous bed of Miocene age. 6.1. MONTMORILLONITE

In Japan, there are two kinds of clay deposits containing montmorillonite as a main constituent mineral: one is called bentonite and the other, acid clay. They are employed for entirely different purposes due to their divergent properties. The term acid clay was first applied by Kobayashi (1949) to a clay whose water suspension was found to be acidic. It is utilized as a raw material to produce activated clay, clay for non-carbon paper, etc. by sulfuric acid treatment, and further to produce aluminum sulfate, etc. as by-products. 6.1.1.

Outline of the genesis of bentonite and acid clay deposits

Bentonite and acid clay deposits of major economic importance occur in association with volcanic rocks, tuffs and tuffaceous sediments of Miocene and Oligocene age. Three types of processes have governed the genesis of the bentonite deposits : (1) alteration from rhyolitic ash in a marine environment and subsequent diagenetic alteration, (2) hydrothermal alteration from rhyolite and rhyolitic tuff, and (3) hydrothermal alteration of rhyolitic ash and pumice 221

222

SMECTITES

in a marine environment. In the case of Na-bentonite deposits, two types of occurrence have been reported : (1) regional bentonite beds intercalated in sediments, and (2) bentonite deposits forming irregular masses with lateral extensions. The former type may have been formed by chemical alteration of rhyolitic ash accumulating in a marine environment as it settled through sea water, followed later by diagenetic alteration. The latter type was formed by hydrothermal alteration of rhyolite and rhyolitic tuff. It seems likely that much of the original silica and alkali was leached from the rhyolitic ash, tuff and other rocks by solution during alteration. The exchange cation of montmorillonite is composed principally of Na+. A few deposits of (Ca,Mg)-bentonite are now mined at the open pits of Kawasaki and Zao, Miyagi Prefecture. However, detailed geological and mineralogical studies on these deposits have not yet been made, and further descriptions are not included here. In the case of acid clay deposits, two types of occurrence have been reported: (1) thick and lenticular acid clay beds intercalated in sediments, and (2) acid clay deposits forming masses with lateral extensions. The former type may have been transformed by supergene weathering from montmorillonite deposits which had been formed by hydrothermal alteration of rhyolitic ash and pumice in a marine environment. The latter probably arose from montmorillonite deposits which had been formed by hydrothermal alteration from rhyolitic tuffs and tuff breccias. The main exchange cations are thought to have been Mg2+ and Ca2+ at the outset of montmorillonite formation, whereas under the subsequent warm and humid climatic conditions following uplift, the deposits were altered by supergene weathering. The exchange cations, Mg2+ and Ca2+, would have been largely leached out and replaced by H+ at the beginning of weathering. As weathering progresses, montmorillonite changes to “abnormal” montmorillonite (Greene-Kelly, 1957), which gives endothermic peaks at both 600°C and 700°C in the dehydroxylation region on its DTA curve, and then the montmorillonite lattice is partially destroyed. There is conversion to (H, Mg,Ca)-montmorillonite/halloysitemixed-layers, and finally transformation to halloysite. 6.1.2. Distribution of montmorillonite deposits

The distribution of the major montmorillonite deposits in Japan is summarized in Table 6.1. The greater part of the montmorillonite deposits clearly occur in the Green Tuff regions (Hokkaido, Tohoku, central Honshu, Shimane), where volcanic rocks and related pyroclastic rocks of Miocene age occur extensively. Bentonite deposits of Miocene age, formed from volcanic ash by chemical alteration in a marine environment during settling through sea water and subsequent diagenesis, occur on the green tuff beds at Oe (Yamagata Prefecture), and in the vicinity of‘Annaka and surrounding areas (Gunma Prefecture), etc. Two bentonite deposits of hydrothermal origin formed from rhyolite and

TABLE 6.1. Major montmorillonite deposits in Japan Location Oe (Yamagata) Annaka, etc. (Gunma) Mikawa (Niigata) Mikawa (Niigata) Mizumaki (Fukuoka)

Parent rock Genesis Main exchange cation Geologic age Volcanic ash Type BI Na+ Miocene Volcanic ash Type BI Na+ Miocene Bentonite Rhyolite Type B2 (n.d.) Miocene Rhyolitic tuff Type €32 Na+ Miocene Volcanic ash Type B1 Na+ Oligocene Volcanic ash Tsuruoka (Yamagata) Type Al Mgzi-, Ca2+,H+ Miocene Acid clay and pumice Volcanic ash Nakajo (Niigata) Type Al Mgz+, Ca2+, H+ Miocene and pumice Shibata (Niigata) Tuff and tuff breccia Type A2 Mgz+, Ca2+, H+ Miocene Omi (Niigata) Tuff and tuff breccia Type A2 (n.d.) Miocene Type B1: alteration from rhyolitic ash in a marine environment and subsequent diagenesis. Type B2: hydrothermal alteration from rhyolite and rhyolitic tuff. Type Al : transformation by supergene weathering from montmorillonite deposits formed by previous hydrothermal alteration of rhyolitic ash and pumice in a marine environment. Type A2: transformation by supergene weathering from montmorillonite deposits formed by previous hydrothermal alteration of rhyolitic tuff and tuff breccia.

224

SMECTITES

rhyolitic tuff, respectively, occur at Mikawa (Niigata Prefecture). A bentonite deposit formed by chemical alteration of volcanic ash in a marine environment and subsequent diagenesis, occurs on the sediments of Oligocene age at Mizumaki (Fukuoka Prefecture). Acid clay deposits occur as thick lenticular beds on sediments of Miocene age at Tsuruoka (Yamagata Prefecture) and Nakajo (Niigata Prefecture). They may have been transformed by supergene weathering from (Mg,Ca)-montmorillonite deposits derived from volcanic ash and pumice by hydrothermal alteration in a marine environment during the Miocene. Acid clay deposits forming massive bodies with lateral extensions exist at Shibata and Omi (Niigata Prefecture). They are thought to have been transformed by supergene weathering from (Mg,Ca)-montmorillonite deposits formed from tuff and tuff breccia of Miocene age by hydrothermal alteration below the surface of the sea bottom. Brief details of the above-mentioned deposits are given next. A. Bentonite deposits of Yamagata

The bentonite beds at Oe constitute one of the major bentonite deposits now being mined in Japan. This deposit occurs on sediments of Miocene age. Hayakawa (1961) and Honda (1962) have described its general geology and mineralogy. The bentonite beds form part of many tuffaceous strata intercalated with a hard shale formation. The thickness of the bentonite beds now being mined is 1-2 m, except for one reaching 7 m. Honda (1974) has stated that the swelling capacity of this bentonite is higher than that of material from other localities in Japan. Although it is common for cristobalite to occur as an impurity in bentonites from other localities, quartz is here contained in the bentonite instead of cristobalite. Honda (1974) has suggested from observations of the occurrence of montmorillonite and zeolites in this deposit, that the montmorillonite has been transformed from zeolites which were previously derived by alteration from vitro-clastics in pyroclastic rocks. B. Bentonite deposits of Gunma

In the southern part of Gunma Prefecture, marine Tertiary sediments are extensively distributed and many tuffaceous sediments are intercalated with them. These tuffaceous sediments contain a number of bentonite deposits. Kizaki (1960, 1963) has described the geology of the district where the bentonite deposits are found. Most of the tuffaceous beds have been altered, and some have undergone conspicuous argillaceous alteration. Although alteration products such as celadonite, clinoptilolite, analcime, etc. also occur, montmorillonite is the most extensively distributed mineral and is included in almost all the tuffaceous beds. Bentonite deposits of economic importance occur in the vicinity of Annaka and in the surrounding areas. These bentonites include cristobalite and carbonate minerals (mainly calcite) as impurities. The main exchange cation is Na+.

MONTMORILLONITE

225

C. Bentonite deposits of Niigata

In this area, Neogene Tertiary rocks unconf‘ormably overlie the basement which consists of “Chichibu” Paleozoic sediments and granodiorite (Fig. 6.1). Fujita (1949) has summarized the stratigraphy of the area as follows:

J Nanatani (Awase) member (bentonite deposits) Miocene\Tsugawa member Paleozoic sediments and granodiorite The two bentonite deposits at Mikawa occur, respectively, on rhyolite and rhyolitic tuff belonging to the Nanatani (Awase) member. Takeshi (1963) has described the geology of these deposits and studied the mineralogy and chemical properties of the bentonites by optical microscopy, X-ray diffraction and chemical methods, etc. Kanto bentonite deposit: The Kanto bentonite deposit was formed from rhyolite by hydrothermal alteration. In the intensely altered zone, the groundmass of the original rock is usually altered to very fine fibrous or lamellar montmorillonite and cristobalite aggregates, whereas phenocrysts of quartz remain unaltered and plagioclase phenocrysts as well as a small quantity of biotite are observed by optical microscopy. In the weakly altered zone, silicification is conspicuous and the groundmass is almost completely altered to quartz except for a small quantity of biotite. Teikoku bentonite deposit: The Teikoku bentonite deposit is a massive deposit with lateral extensions, formed by hydrothermal alteration of rhyolitic tuff. The principal constituent mineral is montmorillonite, and cristobalite occurs as an impurity. Phenocrysts of quartz and plagioclase from the original rock remain in an unaltered state. The main exchange cation is Na+. D. Bentonite deposit of Fukuoka

Sakamoto (1970) has described the geology, mineralogy and other properties of the bentonite deposit in Fukuoka Prefecture which is widely distributed in the northern part of the Chikuho coalfield. The total thickness of the whole sequence of bentonite beds is approximately 100 m in the Onga Formation of the Oligocene. Five or six seams of bentonite are workable, each of which has a thickness of 2.5 to 5 m. A geologic profile of the main bentonite seams is given in Fig. 6.2. The main constituent mineral is Na-montmorillonite with quartz, feldspar and sericite occurring as impurities. Only two out of the bentonite seams contain additional cristobalite. The CEC’s of the bentonites range from 80 to 100 meq/100 g, and 70 to 80% of the total exchange cation is Na+. E. Acid clay deposits of Yamagata

Takeshi et al. (1969) havc given an outline of the geology and mineralogy of the acid clay deposits at Tsuruoka and at Nakajo (Niigata Prefecture). The de-

226

SMECTITES

km

0

Kanto bentonite

0

Teikoku bentonite Bentonite deposits

tzzzl ml ',:\-I

Tsugawa Formation Paleozoic rocks Rhyolite Awase Formation Tuff and shale

Fig. 6.1. Location of the bentonite deposits at Mikawa, Niigata Prefecture, and a geologic map of the surrounding area (by courtesy of Niigata University; after Takeshi, 1963).

MONTMORILLONITE No. 1

227

100

0

-250

-

200m

/’

Fault

Fig. 6.2. Geologic profile of the bentonite beds at Mizumaki, Fukuoka Prefecture (after Sakamoto, 1970). No. 1-No, 4: main bentonite beds.

posits at Tsuruoka occur on Miocene sediments which consist mainly of rhyolitic pyroclastic rocks and lie unconformably on a basement of granitic rocks of Mesozoic-Tertiary age. F. Acid clay deposits of Niigata

Granitic rocks form the basement in this area and are overlain unconformably by a Miocene sequence comprising the Tsugawa, Nanatani and Teradomari members. The Nanatani member consists mainly of rhyolitic pyroclastic sediments, in which acid clay deposits are intercalated. One of the largest acid clay deposits in Japan occurs at Nakajo. Although acid clay deposits also occur in the Nanatani member at Shibata and Omi, their modes of occurence and genesis are different from those of the Nakajo and Tsuruoka deposits. 6.1.3. Constituent minerals of bentonites

The constituent minerals of the bentonites in all the deposits mentioned above have been determined by optical microscopy, X-ray diffraction analysis, differential thermal analysis, silicate analysis, total cation exchange determinations, exchangeable cation analysis, etc. X-ray diffraction analysis indicates that montmorillonite is the only clay mineral identified with certainty from the bentonites of Gunma and Niigata, whereas those of Yamagata and Fukuoka contain sericite in addition. X-Ray diEraction patterns for air-dried samples of all the deposits closely resemble that of Wyoming montmorillonite. The basal spacing of samples prepared for X-ray analysis by air-drying ranged from 15.5 to 15.0 A. The reflection (06,33) at 1.493 A is identical with that of montmorillonite (e.g. Teikoku bentonite). The non-clay constituents that are visible through the microscope consist of angular grains of quartz, feldspar and some biotite, which were originally phenocrysts in the parent volcanic glass. In the bentonites of Niigata and Gunma,

228

SMECTITES

submicroscopic aggregates of cristobalite derived from volcanic ash, are generally detected by X-ray diffraction determinations. As mentioned, two of the many bentonite beds at Fukuoka contain cristobalite, but this mineral has not been detected in the bentonites of the Yamagata deposits. The bentonites from Yamagata and Fukuoka usually contain quartz. Iron oxides occur in the bentonites of most deposits, and carbonates and zeolites are sometimes found. DTA curves are presented in Fig. 6.3, showing the features of typical Na-montmorillonite. The chemical composition and cation exchange capacities of the bentonites are listed in Tables 6.2 and 6.3, respectively.

0

100

200

300

400

500

600

700

800

900

1000

Temp. ("C)

Fig, 6.3. DTA curyes for bentonites. A, Bentonite from Wyoming, U S A . (after Takeshi and Uno, unpublished data). B, Bentonite from the Teikoku bentonite, Mikawa, Niigata Prefecture (after Takeshi and Uno, unpublished dutu): the exothermic peak at about 500°C is due to the pyrite included in the bentonite). C, Bentonite from Oe, Yamagata Prefecture (after Honda, 1974). D, Bentonite from Mizumaki, Fukuoka Prefecture (after Sakamoto, 1970).

MONTMORILLONITE

229

TABLE 6.2. Chemical composition of bentonites Gunmal) ___ 60.33 % 0.32 17.05 2.09 0.28 0.00 1.58 0.66 1.27 0.23 7.88 8.30 100.00

-~ - .

SiOz Ti02 AlzOz Fez03 FeO MnO MgO CaO Na20 KzO HzO( HzO(-) Total

+>

Yamagata2) 61.06%

Fukuoka3) 61.49%

15.84 2.13

21.44 4.78

2.86 1.46 2.50 0.20 13.98

2.06 1.15 2.62 1.16 5.11

Niigata4) 66.07 % 0.31 11.65 2.00 0.27

Wyoming5) 52.66 % 0.00 19.13 1.96 0.50 0.00 2.37 1.11 1.49 0.13 5.68 14.99 100.02

2.53 0.39 1.32 0.28 4.40 10.30 99.54

99.81 100.03 Bentonites from; 1) Yokokawa, Gunma; after Kizaki (1963). 2) Tsukinuno, Oe, Yamagata; after Honda (1974). 3) Mizumaki, Fukuoka; after Sakamoto (1970). 4) Mikawa, Niigata (Teikoku); after Takeshi and Uno (unpublished data). 5) Wyoming, U.S.A.; after Takeshi and Uno (unpublisheddctu).

TABLE 6.3. CEC values of bentonites (units: meq/100 g ) Yaniagatal) Na+

K+ Mgz+ Ca2+

65.4 1.o 5.6 19.4

Fukuoka

Niigataz) (Teikoku)

64.1 10.1 25.2

55.5 3.1 3.1 10.9

98.2 9.8

73.2 15.6 9.4

85.7

PH

48.0 1.6 13.3 19.8 0.4 83.1 84.0 10.1

-

~ 1 3 +

Total CEC

Wyoming3)

1) Dried at 105°C. 2,3) Air-dried wt. All materials were the same as those used for chemical analysis in Table 6.2.

TABLE 6.4. Constituent minerals of acid clays Source

M

++ ++

Q

MK

+ + +

+

Cr

+ + +

Tsuruoka Nakajo Shibata (Odo) M = Montmorillonite MK = Montmorillonite/ha1loysitemixed-layer mineral Q = Quartz F = Feldspar Main constituent Cr = Cristobalite H = Halloysite Admixed mineral

++

+

++ +

F

+ +

+

H

SMECTITES

230

6.1.4.

Constituent minerals of acid clays

The constituent minerals of acid clays as determined by optical microscopy, X-ray diffraction analysis, etc. are listed in Table 6.4. Montmorillonite is also the main constituent mineral of acid clays. The reflection (06, 33) at 1.498 (a Nakajo specimen) indicates that the montmorillonite is of dioctahedral type. The specimens of acid clay often contain quartz, cristobalite and feldspar as admixed minerals, although the relative abundances of these minerals fluctuate from specimen to specimen. Feldspar tends to be less abundant, and zeolite scarcely occurs. Although the color of the acid clay from the lower part (fresh zone) of the Nakajo deposit is generally blue, the acid clays occurring near the surface and along faults, and the acid clay beds alternating with shale (weathered zone) are yellow. It seems likely that the yellow color of the acid clay in the weathered zone is due to oxidation and hydroxidation of montmorillonite and pyrite. Acid clay specimens of high quality from the Nakajo deposit give the diffraction patterns of montmorillonite, whereas some specimens from medium-weathered zones yield another kind of diffraction pattern with a diffuse basal reflection showing almost no peak profile and a sharp profile of (hk) reflections, such as (11, 02), (13, 20) and (33, 06) (Fig. 6.4). DTA curves for acid clays from the Tsuruoka and Nakajo deposits are given in Fig. 6.5. DTA curves of acid clays from Odo, having typical X-ray diffraction patterns of montmorillonite, exhibit one endothermic peak at 720°C in the dehydroxylation range, However, the curves for clays from Tsuruoka, having diffraction patterns with a very diffuse (001) reflection, exhibit one endothermic peak between 500 and 600°C. The DTA curves of the Nakajo clays can be classified into three groups, with (1) a single peak at about 700”C, (2) a single peak between 500 and 600”C, and (3) a dual peak at about 600 and 700°C.

6.1 S. Transformation of montmorillonite to halloysite by weathering Grim and Bradley (1948, 1953), Greene-Kelly (1957), etc. have studied the dehydroxylation of montmorillonite in the temperature range 500-700°C. The DTA curves of “normal” montmorillonite show one endothermic peak at about 700°C. Some pure dioctahedral montmorillonites (“abnormal” montmorillonites) have been found to give double endothermic peaks at about 600 and 700°C. Many explanations have been given for this. For example, Jonas (1955) has stated that aluminous montmorillonites showing a dual peak at about 600 and 700°C consist of bimineralic mixtures. Greene-Kelly (1957) has pointed out that structural irregularity might be responsible for the double peaks. Grim and Kulbicki (1961) have concluded that the dual peak may well represent some sort of mixing of layers. Sudo and Hayashi (1956) have described certain clays closely associated with acid clay deposits, which showed unusual properties. Their X-ray diffraction patterns consisted of several broad reflections resembling those of montmoril-

231

MONTMORILLONITE

H1

H2

MK t13

. I1 3

*

IMK

H5

(1 1.02)

n 1

lOB7.2A

%\ I

I

I

1

20

10

I

I

(1 1.02j

1

I

10

1

1

20

30'

28

H6

I

30"

28

Fig. 6.4. X-ray diffraction patterns of acid clays and associated clays (after Takeshi and Uno, 1974). Hl-H4: Acid clays from the Nakajo deposit, Niigata Prefecture (H1 and H2, from the weakly weathered zone; H3 and H4, from the medium weathered zone. H5 and H6: Clays transformed (intensely weathered)frorn acid clays at Sanko and Hanezu, respectively, Niigata Prefecture. T1-T3: Acidclays from the Tsuruoka deposit (medium weathered), Yamagata Prefecture. Numbers indicate the order of progression of weathering. M, Montmorillonite; MK, montmorillonite/halloysite mixed-layers; H, halloysite.

lonite or hydrated halloysite. Almost no basal reflections occurred in the range of 0-20" for 28, although the principal prism reflections were clearly apparent. They concluded that the crystallites probably consist of montmorillonitic and kaolinitic layers and that such clays represent an intermediate stage in the alteration of montmorillonite to kaolin or vice versa. Shimoyama and Johns (1969) have concluded that these clays were formed by leaching of montmorillonite by surface or acidic groundwater. Geological observations and petrographic and geochemical investigations on acid clay deposits and related

232

SMECTITES :heto HI H2

H3

H4

H5

H6

l-1 r2 r3

400

! 3

600

700

a 0

Temp. (2)

Fig. 6.5. DTA curves for acid clays and associated clays (after Takeshi and Uno, 1974). Cheto: Montmorillonitefrom Cheto, U.S.A., used as reference material. Other symbols are as in Fig. 6.4.

clay locations (Takeshi et al., 1969; Takeshi and Uno, 1974) suggest that they represent various intermediate stages of transformation of (Mg,Ca)-montmorillonite to halloysite by supergene weathering. We propose the process of formation and weathering of montmorillonite in acid clay deposits illustrated in Fig. 6.6. The altering solution is weakly acidic groundwater enriched with sulfuric acid produced by the oxidation of pyrite. In a marine environment, pyrite is precipitated synchronously with the formation of montmorillonite. “Abnormal” montmorillonite is formed from montmorillonite by the leaching of interlayer cations such as Mg2+and Ca2+and subsequent leaching of Mg2+from octahedral layers and Si4+from tetrahedral layers at the primary stage of weathering as exemplified at the Nakajo deposit. At the second stage of weathering, a halloysite-like layer is created by the leaching of silica layers and replacement of vacant tetrahedral oxygen sites by hydroxyls in the residual 1 :1 sheets, as proposed by Altschuler and Dwornik (1963). Interposition of halloysite-like layers within montmorillonite layers creates a randomly mixed-layer mineral, montmorillonite/halloysite. As the montmorillonite continues to decompose through

23 3

MONTMORTLLONITE Volcanic ash and pumice

Tuff or tuff breccia

marine environment

below the surface of the sea bottom

(Mg, Ca)-Montrno;illonite

- - _ _ _ -. -

.

7.+~

_ _ _ __ _ _ -1- - __ __ % _ _ _ _ _ _ _ _ _ _ _ _ _ ___ ____ 7 ' Medium weathering -I- Intense weathering I

Weak weathering

(Mg, Ca, H)-Montrnorillonite and "abnormal" rnontrnorillo II ite

1

;

:

I

(H, Mg, Ca)-Montrnorillonite/halloysite mixed-layer .

Halloysite 1 I I I

!

Fig. 6.6. Process of formation and weathering of montmorillonite in acid clay deposits.

the alteration process, the halloysite-like layers are nourished by lateral epitaxy. At the final stage of weathering, the primitive halloysite layers are enlarged due to the breakdown of the montmorillonite. The final product of such a weathering process is halloysite, as exemplified at Hanezu and Sanko (Niigata Prefecture). The differences in X-ray diffraction patterns and DTA curves between altered montmorillonites associated with acid clay deposits and typical montmorillonites, thus appear to be explained by a defect structure, a mixedlayering between montmorillonite/halloysite and/or halloysite, all of which have been transformed from montmorillonite during weathering.

Cheto

H1 H2 H3

H4 H5

H 6

3700 3600 Wave number fcm-')

3700

3600

Wave niimher lorn-'\

Fig. 6.7. Infrared absorption spectra in the OH region of acid clays and associated clays (after Takeshi and Uno, 1974). The same materials as in Figs. 6.4 and 6.5 were used.

234

SMECTITES

X-ray diffraction patterns, DTA curves and hydroxyl absorption bands of infrared spectra for selected samples arranged in order of transformation by weathering, from the Nakajo deposit of acid clay and related clay locations (Fig. 629, are illustrated in Figs. 6.4, 6.5, and 6.7, together with those for material from the Tsuruoka deposit. As (Mg,Ca)-montmorillonite continues to decompose, the profiles of the basal (001) reflections of montmorillonites in the X-ray diffraction patterns become less pronounced and more diffuse in the order of sample number, and in extremely altered samples, (H5 and H6), the (001) reflection of halloysite appears. Moreover, the endothermic peaks at about 600°C (caused by defect structure and/or halloysite layers) become more pronounced, and those at about 700°C (caused by montmorillonite layers) become less pronounced. In extremely altered samples, almost no montmorillonite peak is found on the X-ray diffraction patterns and DTA curves. The infrared spectra also become progressively closer to that of halloysite. The chemical composition, cation exchange capacities and Si/Al ratios calculated from the chemical composition, etc. for the same samples as those used for X-ray analysis, etc. from the Tsuruoka deposit, are listed in Table 6.5. The .TABLE 6.5. Chemical analyses and cation exchange capacities of acid clays from Tsuruoka, Yamagata Prefecture (air-dried wt; after Takeshi and Uno (1971)) Sample No.

SiOz Ti02 A1203 Fez03 FeO MnO MgO CaO Na2O KzO HzO(+) H2O(-)

Total PH CEC (meq/100 g) Ca2+ Mg2+

Naf K+ ~ 1 3 +

Total Si/Al ratio

1(T-1) 50.08 % 0.47 15.78 5.34 0.01 0.14 3.51 0.90 0.29 0.44 8.53 14.46 99.95

2(T-2) 46.15% 0.48 18.41 5.60 0.03

3 46.30% 0.48 18.65 5.12 0.03

3.40 0.14 0.24 0.33 9.05 16.10 99.93

3.29 0.03 0.24 0.34 9.04 16.44 99.96

5.5 87.0 33.4% 29.4 1.1 1.1 0.6 65.6

4.9 65.4 7.1 % 17.1 1.5 1.8 0.1 27.6

4.8 -

5.38/2

-

4.2512

-

-

-

4.2112

4(T-3) 47.68 % 1.92 20.03 5.45 0.03 2.48 0.24 0.38 0.24 7.96 13.52 100.38 4.8 58.3 7.3 % 5.3 2.3 12 0.7 16.8 4.0412

235

MONTMORILLONITE

0

2

4

\

[mI

Nanatani Formation

Liparite

A

"Acid clay" deposit

X

Location of weathered niontrnorillonite clay

Fig. 6.8.

Location map of the Nakajo acid clay deposit and related clays.

gkrn

236

SMECTITES

Si/Al ratios become progressively smaller with decrease in CEC's and pH values, in accordance with the changes in X-ray diffraction pattern, DTA curve and infrared spectrum, as montmorillonite continues to decompose by weathering. 6.1.6. Montmorillonitelhalloysite mixed-layer mineral

For investigation of the variations in C-axis spacing, two specimens, H1 and H4, representing different stages of weathering at the Nakajo acid clay deposit, with Cheto montmorillonite as reference, have been saturated with sodium, magnesium and calcium ions, respectively. Some of the variations in c-axis spacing of the constituent clay minerals with sodium as an exchange cation at different relative humidities are illustrated in Fig. 6.9. The spacing and profile of the basal reflection of specimen H1 is close to that of the Cheto montmorillonite at each relative humidity. However, the spacing of the basal reflection of specimen H4 is much smaller than that of the Cheto montmorillonite, especially at low relative humidity. The profile of specimen H4 at lower relative humidity is more pronounced than that at higher relative humidity, in contrast to the case of the Cheto montmorillonite. The effects on the c-axis spacing of the same materials, following hydrazine intercalation, are illustrated in Fig. 6.10. Weiss et al. (1963) have reported the effective intercalation of hydrazine into kaolinite, and Wada and Yamada (1968) have proposed procedures for hydrazine intercalation in the case of kaolin minerals. Intercalation of kaolin minerals with hydrazine results in a shift in H4-Na 15.0 7.2i

H 1-Na 15.0 7 . 2 i

Cheto- Na

15.0

7.2i

I

4L

R.H. 70 %

$L

R.H. 40 %

R.H.1096

rl -5

10

28

15"

5

10

28

15"

u 5 10 15' 28

Fig. 6.9. Variations in the basal spacing of specimens H1 (weakly weathered), H4 (medium weathered) and the Cheto montmorillonite, with Naf ion at various humidities. The same materials as above were used (after Takeshi and Uno, 1974). R.H. = relative humidity.

SAPONITE

237 Cheto-Na

U.t.

15.0

7.2 A

H 4- Na

HI-Na

hydr. 15.0 10.4 7.2

u.t. 15.0 7.2A

hydr. 15.0 10.4 7.2 A

hydr.

u.t.

15.0

7.2i

15.0 10.4 7.2 1

1

I

12.0

u 5

10

15'

213

5

10

213

15"

5

10

28

15"

5

10

213

15"

5

10

213

15'

5

10

15'

213

Fig. 6.10. Basal reflections of X-ray diffraction patterns, showing the effect of hydrazine intercalation on the same materials as in Fig. 6.9 (Takeshi and Uno, unpirblislreddura).R.H. = relative humidity; u.t. = untreated; hydr. = hydrazine intercalation.

their 7 A basal diffraction peak to 10 A. The basal spacing of specimen H4 became distinctly larger on treatment by hydrazine intercalation, whereas that of specimen H1 as well as that of the Cheto montmorillonite remained almost unchanged. It has been concluded, therefore, that the constituent clay mineral of specimen H4 is a randomly mixed-layer mineral montmorillonite/halloysite. 6.2. SAPONITE

Iron-rich saponite occurs widely as a cementing material of iron sand deposits of Tertiary age. Although Sudo (1943) originally proposed the name "lembergite" for this material from the iron sand deposit at Moniwa (Miyagi Prefecture), it was later identified as a variant of saponite (Sudo, 1954). Iron-rich saponite also occurs in glassy rhyolitic tuffs at Oya (Tochigi Prefecture). The material identified as iron-rich montmorillonite (Sudo and Ota, 1952), is composed of an intimate mixture of two kinds of smectites: iron-rich saponite and montmorillonite-beidellite with medium amounts of Fe and Mg (Koyama et al., 1972). The deep green mineral coating the inner walls of the druse and amygdaloidal cavities of the slightly altered basalt at Yamashiro (Saga Prefecture) has been identified as iron-rich saponite by Muchi and Higashiyama (1972). Kimbara and Shimoda (1972) and Kimbara (1975) have described the occurrence and mineralogy of iron-rich saponite associated with other ferromagnesian clay minerals occurring as alteration products of basic/medium pyroclastic rocks at Taiheizan (Akita Prefecture) in the Green Tuff region of Neogene Tertiary age. The chemical composition and structural formulae of iron-rich saponites are

23 8

SMECTITES

listed in Table 6.6. The ideal structural formula may be written Mi.67(Mg6) (Si7.33A10.67)0~~(0H)4, while the ideal structural formulae of the iron-rich saponites at Oya and Moniwa may be written in their ferrous forms as follows: Mi.6 d M g ~ F e i ~ (si7.33A10.67)020(0H)4 ) (@a), and Mi.s7(Mg3Feit)(Si7.33 A10.67)020(0H)4 (Moniwa). Koyama et al. (1972) have stated that these formulae strongly suggest the existence of an iron analog of saponite corresponding to the ideal formula: M;,,(Fei+) (Si7.33A10. 67)020(0H)4. DTA curves for certain iron-rich saponites are illustrated in Fig. 6.11. They show the usual features of smectites : a pronounced endothermic peak due to dehydration, an endothermic peak due to dehydroxylation, an endothermic peak TABLE 6.6. Chemical composition and cation exchange capacity of saponites

Si02 TiOz A1203

Fez03 FeO MnO MgO

CaO NazO

KzO

fixed exch. fixed exch. fixed exch. fixed exch.

Taiheizanl) 40.53 % 0.20 12.20 8.79 4.20 0.20 14.19 0.25 0.81 2.43 0.36 0.12 0.85 0.19 7.44 8.30 101.04

Moniwaz) 39.68 % 0.37 3.93 19.82 1.12 0.19

Yamashiroa) 48.29 % 0.10 7.50 1.46 6.60

11.21

19 88

18.02

7.6

2.37

1.31

2.78

2.3

L

-

Maze4) 43.98 % 0.16 6.30 7.85 5.32 0.32

oya5) 35.5 % 7.9

-

26.6

-

1.7

-

0.2 HzO(+) 6.16 9.40 9.24 HzO(-) 15.11 5.58 6.24 Total 99.96 100.12 100.39 81.8 Residual* 18.2 * This value is considered to represent the amount of interlayer water and structural water. CEC (meq/lOO g) 120 Ca 43 Mg 6 Na 4 K 4 Total (meq/100 g) 57 1) Taiheizan, Akita; after Kimbara (1975): (Ca0.268Nao.07~Ko.102)(Mgi.65, FeZ,+27iFelZin Abz35) (Si3.iy A ~ o . s ~ ~ ) ~ ~ o ( O H ) ~ ~ H , O . 2) Moniwa, Miyagi; after S u d o (1954): Can.23(Mgi.5, FeG5 Alo.04) (Sj3.62 Alo.dOio(OHI,. 3) Yamashiro, Saga; after Muchi (1972): Ca0.15 ( M g 2 . 1 7 FeZo FeO3:'os &.is) (Si3.54 &.4tj)oio(oH)~. 4) Maze, Niigata; after Miyamoto (1957). 5) Oya, Tochigi; after Koyama et al. (1973); analyzed by EPMA: (Nao.60K0.44 Cao.44) (Mg2.04Fe& AIo.od (sis.36 A11.64)02o(OH)4.

NONTRONITE

239

I

/

f

0

100

200

300

400

500

I

I

700

800

900

1 30

Temp. ("C)

Fig. 6.11. DTA curves for iron-rich saponites. A, from Oya, Tochigi Prefecture (Koyama et a[., 1973); B, from Yamashiro, Saga Prefecture (Muchi and Higashiyama, 1971); C, from Taiheizan, Akita Prefecture (Kimbara, 1975).

between 800 and 900°C and a small exothermic peak at about 9OO"C, although the endothermic peak due to dehydroxylation and the exothermic peak at about 900°C are scarcely visible in the Yamashiro specimen. 6.3. NONTRONITE

The yellowish clayey material found in alteration products of basalt at Yamashiro (Saga Prefecture) has been identified as nontronite by Muchi (1975). It occurs as a veinlet with a width of a few centimeters, which is thought to represent decomposed basalt formed by the action of low temperature ascending water. Although the X-ray diffraction pattern shows the features of smectite, the refractive indices are higher than those of montmorillonite, viz. a = 1.570, y = 1.601. The DTA curve, which is close to that for nontronite described by Grim and Rowland (1942), has an endothermic peak at about 500°C and an exo-

SMECTITES

240

thermic peak at about 900°C, as shown in Fig. 6.12. Results of chemical analysis and the general formula are given in Table 6.7. 8

*

0 F

Fig. 6.12. DTA curve for nontronite from Yamashiro, Saga Prefecture (after Muchi, 1975).

TABLE 6.7. Chemical composition and formula of nontronite from Yamashiro, Saga SiOa Ti02

41.56 % 0.17 11.35 22.48 0.62 0.01 1.02 2.23 0.35 0.33 20.45

Total

99.62

6.4. STEVENSITE

The synthetic Mg smectite, (Si8)(Mg5.84)020(0H)4,has been synthesized by 1 M; 33 Strese and Hofmann (1941). Also, Faust and Murata (1953) have found the natural mineral, stevensite, which is substantially the same as the material prepared by Strese and Hofmann. In Japan, Otsu et al. (1963) have reported the occurrence of stevensite asso-

STEVENSITE

241

ciated with various kinds of skarn minerals in a lead-zinc deposit formed by alteration of a calcareous bed of Miocene age at the Ohori mine (Yamagata Prefecture). The stevensites occur as clayey aggregates or aggregates of minute fibrous crystals. Otsu et al. classified the minerals into two kinds; stevensite I (clayey aggregates) and stevensite I1 (fibrous crystals). The X-ray diffraction pattern of stevensite I dried in room air has basal reflections at 15.5 A (OOl), 5.2 A (003) and 3.1 8, (005), and so displays the usual characteristics of smectite. The (001) peak shifts to 17 8, on treatment with ethylene glycol. The (06, 33) peak at 1.52 8, indicates trioctahedral smectite. The material fully dried at a vapor pressure o f 3 mm Hg exhibits a 25 reflection on its X-ray diffraction pattern, as described previously by Brindley (1955). Stevensite I1 shows a someTABLE 6.8. Chemical composition and formula of stevensites

SiOz Ti02 A1203

Fez03 FeO MnO MgO CaO NazO KzO HzO(+) HzO(-) F Total

1) 57.30%

-

none 0.32 none 0.21 27.47 0.97 0.03 0.03 7.17 6.69

none 100.19

2) 51.18% 0.02 0.48 0.43 0.00 1.60 23.96 2.80 0 08 0.01 8.90 10.18

-

99.64

Stevensites from : 1) Springfield, N. J.; after Faust and Murata (1953). 2) Ohori mine; after Otsu et al. (1963). Formula of the unit-cell layer of stevensite from the Ohori mine: (Mg, 46 Mno 22 Fe% Feo2'od (Si, 84 AIo 10)0Z0(0H)4 (Cao 44 Nao o~ KOoo)."HzO

-

what different X-ray diffraction pattern from stevensite I. It has random mixedlayer characteristics, with a very diffuse basal reflection at 11-12 A. The chemical composition of stevensites and the formula of the stevensite from the Ohori mine are given in Table 6.8. The data suggest a defect structure in which the sum of the octahedral cations in the formula is below 3.

242

SMECTITES

REFERENCES Altschuler, 2. S., Dwornik, E. J. and Kramer, H. (1963) Science 141, 148. Brindley, G. W. (1955) Amer. Miner. 40, 239. Faust, G. T. and Murata, K. J. (1953) Amer. Miner. 38,973. Fujita, K . (1949) J . Geol. SOC.Japan 55, 199. Greene-Kelly, R. (1957) The Differential Thermal Analysis of clays, p . 140-164, Miner. SOC.London. Grim, R. E. (1953) Clay Mineralogy, McGraw-Hill. Grim, R. E. and Bradley, W. F. (1948) Amer. Miner. 33, 50. Grim, R. E. and Kulbicki, G. (1961) Amer. Miner. 46, 1329. Grim, R. E. and Rowland, R. A. (1942) Amer. Miner. 27, 746. Hayakawa, N. and Shimazaki, K. (1961) Industrial Mineral Resources of Tohoku,Japan, vol. 1, p. 169173, Commission of Development and Investigation on Industrial Mineral Resources of Tohoku. Honda, S. (1962) Industrial Mineral Resources of Tohoku, Japan, vol. 2, p . 101-108, Commission of Development and Investigation on Industrial Mineral Resources of Tohoku. Honda, S. (1974) Rept. Res. Inst. Underground Resources Mining Coll. Akita Univ. 42, 12. Jonas, E. C. (1955) Natl. Acad. Sci. Publ. No. 395,66. Kimbara, K. and Shimoda, S. (1972) J. Clay Sci. SOC.Japan 12, 133. Kimbara, K. (1975) Contributions to C h y Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 42. Kizaki, Y. (1960) Advances in Clay Science, vol. 2, p . 146, Gihodo. Kizaki, Y. (1963) Advances in Clay Science, vol. 5, p . 253, Gihodo. Kobayashi, K. (1949) Acid Clays, Maruzen. Koyama, N., Shimoda, S. and Sudo, T. (1973) Clays Clay Miner. 21, 229. Miyamoto, N. (1957) Miner. J. 2, 193. Muchi, M. (1975) Contributionsto Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 123. Muchi, M. and Higashiyama, K. (1971) Bull. Fukuoka Univ. Educ. Part 111, 21, 151. Otsu, H., Shimazaki, Y. and Ohmachi, H. (1963) Bull. Geol. Surv. Japan 14, 591 Sakamoto, M. (1970) J. Cluy Sci. Japan 10,39. Shimoyama, A., Johns, W. D. and Sudo, T. (1969) Proc. Intern. Clay Conf. Tokyo 1969,1,225. Strese, H. and Hofmann, U. (1941) Z. Anorg. Chem. 247, 65. Sudo, T. (1943) Bull. Chem. SOC.Japan 18, 281. Sudo, T. (1954) J. Geol. SOC.Japan 60, 18. Sudo, T. and Hayashi, H. (1956) Nature 178, 1115. Sudo, T. and Ota, S. (1952) J. Geol. SOC.Japan 58,487. Takeshi, H. (1963) Bull. Geol. Survey Japan 14, 29. Takeshi, H., Fujii, N. and Fujinuki, T. (1969) Proc. Intern. Clay Conf. Tokyo 1969,1, 369. Takeshi, H. and Kato, C. (1969) Clays of Japan, p. 103-120, Geol. Survey Japan. Takeshi, H. and Uno, Y. (1971) Miner. SOC.Japan Spec. Pap. 1, 98. Takeshi, H. and Uno, Y. (1974) J. Miner. Soc. Japan, 11, 162. Takeshi, H. and Uno, Y. (1977) J. Miner. SOC.Japan, 13, 124. Wada, K. and Yamada, H. (1968) Amer. Miner. 53, 334. Weiss, A., Thielepape, W., Ritter, W., Schaffer, H. and Goring, G. (1963) Z. Anorg. Allgem. Chenz. 320, 183.

Chapter 7 Chlorite minerals

Haruo SHIROZU

Chlorite minerals form a group of hydrous silicates whose fundamental unit layer consists of a 2:l layer and an interlayer hydroxide sheet. These minerah occur quite extensively in various rocks and clays in Japan, and vary widely in their mineralogical properties. They can be subdivided into two series of trioctahedral and dioctahedral minerals on the basis of the character of the octahedral sheet in the 2:l layer of the structural unit of the chlorite. The trioctahedral series is characterized chemically by Fe and Mg, and the dioctahedral series by Al. Part of the interlayer hydroxide sheets of both series is often substituted by water molecule sheets in varying proportions, i.e. interstratified minerals with smectite or vermiculite are formed. Of the various chlorite minerals with diverse modes of occurrence in Japan, those of most striking interest from the viewpoint of clay mineralogy are found in tufTaceous sediments, altered wall rocks of Kuroko deposits, and hydrothermal metallic ore veins. Hydrothermal processes are closely related to the formation of these minerals. In this Chapter, the striking chlorite minerals, i.e. the genuine chlorites and minerals close to chlorite, are described. Their chemical and X-ray properties and modes of occurrence are emphasized, although at the beginning of the description, some of the macroscopic, representative chlorites found in actual rocks are briefly reviewed. The majority of the minerals close to chlorite are regarded as irregularly interstratified minerals with small amounts of smectite or vermiculite. Regularly interstratified minerals are described in Chapter 8. 7.1. OUTLINE OF TRIOCTAHEDRAL CHLORITE MINERALS

Trioctahedral chlorite mineraIs occur in most kinds of rocks and metallic ore deposits in Japan. They may be classified chemically into Fe-, FeMg- and Mgchlorite minerals according to the ratio of Fe/(Fe Mg). The boundaries separating the three groups may be conveniently set at ratios of 0.7 and 0.3, respectively. FeMg-chlorite minerals occur most extensively as constituents of low-grade schists and sedimentary rocks, as alteration products of mafic minerals in igne-

+

243

CHLORlTE MlNERALS

244

ous rocks, and also as gangue or wall-rock alteration minerals of metallic ore deposits. Mg-chlorites containing small amounts of Fe are the next most widespread, and are found in association with serpentine or talc. Cr-bearing Mgchlorite (kammererite) is found in association with chromite in serpentinized ultrabasic rocks. Mg-chlorites also occur in some metallic ore deposits. Magnesian chlorite clay minerals poor in Fe are characteristically found in the wall rocks of Kuroko deposits of subvolcanic origin. In contrast, Fe-chlorites are common in hydrothermal metallic ore veins which are also believed to be of subvolcanic origin. The trioctahedral chlorite minerals mostly occur as macroscopic or relatively coarse grains. These well-crystallized chlorites are considered to belong to the orthochlorite of Tschermak (Shirozu, 1958a, 1960). The chemical formula is [(Mg, Fe2+)6-z(A1, Fe3+),] [Al, Si4-zl 01~(0H)8. Fine-grained chlorite minerals as represented by Kuroko chlorite can be regarded as belonging to the leptochlorite of Tschermak, in which some octahedral cations are deficient due to substitution of 2A1 for 3Mg in addition to the substitution of 2A1 for SiMg in orthochlorite. The fine-grained minerals often form interstratified structures with expandable layers, which may also be regarded as a kind of leptochlorite. The polytype of the trioctahedral chlorites is usually IIb, but Ib (P = 90") and Ib (P = 97") are common in Fe-chlorites. Ib ( p = 90") and Ia are occasionally identified in Mg-chlorites. 7.2. THE FeMg-CHLORITES OF SCHISTS AND Mg-CHLORITES OF SERPENTlNlTES AND CERTAlN METALLIC ORE DEPOSITS

The FeMg-chlorites of low-grade crystalline schists and Mg-chlorites associated with serpentinites are representative, well-crystallized chlorites found in rocks, and a number of studies have been made. The chemical composition of the chlorites in schists was first discussed by Miyashiro (1957), who considered them to be leptochlorite. However, subsequent studies by Shirozu (1958a), Banno (1964) and Horikoshi (1965) on chlorites from the Sanbagawa schists in Shikoku indicated that most metamorphic chlorites consist of orthochlorite. Shirozu (1969) has summarized the chemical composition of the chlorites in schists, including chlorites associated with cupriferous pyrite deposits in schists, together with that of the chlorites in serpentinites, as shown in Fig. 7.1. The plots are based on chemical analyses and X-ray measurements of the cell dimensions. It is apparent that substitution of tetrahedral A1 for Si is limited to a considerably narrow range, and there is a clear trend for increasing tetrahedral A1 substitution to be accompanied by a corresponding increase in octahedral Fe. Compositional variations exist among chlorites with different modes of oc-

FeMg-CHLORITES AND Mg-CHLORITES 1.(

I

245

1

0 1

0 2

.3 0 4 .5

0 0 0

0

8,

I

00'5

176

m 7

I

1.o 1.5 Al in 4 (Si, At)

Fig. 7.1. Chemical compositions of chlorites in schists and serpentinites (Shirozu, 1969). 1) From a bedded cupriferous pyrite deposit in schist. 2) From pelitic schist. 3) From basic schist. 4) From quartzose schist. 5) Chlorite rock along a serpentinite/schistboundary. 6) Chlorite rock in serpentinite. 7) With talc in serpentinite.

currence as described below. The polytype shown by the powder patterns is

IIb. 7.2.1. FeMg-chlorites in schists

The results of studies by Shirozu (1961), Banno (1964), Horikoshi (1965) and Kanehira (1967) have indicated that the Fe/(Fe Mg) ratio of the chlorites in schists is usually in the range from 0.3 to 0.6, and the number of tetrahedral A1 atoms (x in the above formula) is 1.2 to 1.4 in 4 positions (Fig. 7.1). These chlorites may well be called ripidolite. The chlorites coexisting with muscovite, garnet, etc. in pelitic schists contain more Fe than those coexisting with epidote, amphibole, etc. in basic schists. The Fe occurs mostly as Fez+,but small amounts are interpreted to have occur red originally as Fe3+ substituting for octahedral Al, and there is a tendency for the content of Fe3+ to be larger in the chlorites of basic schists (Banno, 1964; Horikoshi, 1965). It is noteworthy that the contents of Fe2+,Fe3+and Mg in these chlorites show a parallel relation to the contents of these components in the host rocks. A similar chemical relation is recognized from the fact that the chlorites associated with bedded cupriferous pyrite depo-

+

246

CHLORITE MINERALS

sits in schists are relatively rich in Fe. Data for chemical analyses of FeMgchlorites are given in Table 7.1, Nos. 1-3. 7.2.2. Mg-chlorites associated with serpentinites

Mg-chlorites associated with serpentinites usually contain small amounts of Feyand their content of A1 is relatively low (x = 0.9-1.25, Fig. 7.1). The following minor variations in chemical composition which bear a close relation to the respective modes of occurrence, have been recognized among chlorites from southwestern Japan (Shirozu, 1969). (1) The composition of chlorites forming chlorite rocks with a phyllitic appearance, which occur along boundaries between serpentinite and schist, is near to that of the chlorites in the schists. (2) The chlorites forming scaly aggregates associated with talc have relatively low A1 TABLE 7.1. Chemical analysis of FeMg-chlorites in schists and Mg-chlorites in serpentinites

SiO2 Ti02 A1203

Fez03 FeO MnO MgO CaO NazO KzO HzO(+) HzO(-) Total

Tetr.

Si A1

1) 24.45 % 0.21 21.99 2.08 28.04 0.54 11.90 tr 0.08 0.17 30.75 0.40 100.61

2) 27.31 % 0.22 19.69 3.23 18.58 0.27 19.01 0.58 0.20 0.02 11.12 0.32 100.55

3) 26.04% 19.96 1.85 21.34 0.47 18.56

4) 29.71 % 19.75 0.29 6.59 0.30 30.79 tr

5) 32.27 % 14.99 1.56 6.89 0.09 31.75 tr

11.62 0.16

12.55 0.14

12.84 0.36

100.12

100.75

-

(100.00)

No. of cations on the basis of 14 oxygens 2.592 2.78 2.694 1.408 1.22 1.306

2.844 1.156

3.096 0.904 0.791

A1 1.339 1.071 1.14 1.127 0.02 Ti 0.016 Fe3+ 0.166 0.25 0.144 0.021 0.113 Uct. Fe2+ 2.485 1.58 1.846 0.527 0.553 Mn 0.048 0.024 0.008 0.02 0.041 2.88 2.860 4.390 4.537 Mg 1.879 Total 5.933 5.89 6.018 6.033 6.002 1) FeMg-chlorite in pelitic schist, Uchiyoke, Niihama, Ehime Prefecture (Banno, 1964). 2) FeMg-chlorite in basic schist near the Sazare mine, Ehime Prefecture (Horikoshi, 1965). 3) FeMg-chlorite associated with a bedded cupriferous pyrite deposit of the Besshi mine, Ehime Prefecture (Shirozu, 1958a). The analysis is corrected for 0.9 % calcite impurity. 4) Mg-chlorite in serpentinite, Sanno, Fukuoka Prefecture (Shirozu, 1958a). 5 ) Mg-chlorite forming a vein accompanying talc in serpentinite, Okushi, Nagasaki Prefecture (Shirozu, 1958a).

Fe- A N D FeMg-CHLORITES OF ORE VEINS

247

contents (corresponding to pennine). (3) The chlorites forming massive chlorite rocks, which occur as veins or lenses in serpentinites, tend to have higher A1 contents (corresponding to clinochlore). Data for chemical analyses of Mgchlorites are given in Table 7.1, Nos. 4 and 5. In addition to these common Mg-chlorites, two unusual Mg-chlorites with low A1 contents are known from serpentinites. One is the exfoliating Mg-chlorite described by Shimane and Sudo (1958) from a vermicuIite deposit accompanying talc. The flakes show remarkable exfoliation on heating, and the mineral was considered to be a chlorite that deviated slightly to vermiculite. The second unusual Mg-chlorite is that described by Shirozu (1958b) from a serpentinite. It is poorly crystalline, with a Ib (P = 90") layer, and occurs as close mixtures with aluminian serpentine. 7.2.3. Mg-chlorites in some metallic ore deposits Well-crystallized Mg-chlorites are also found in some metallic ore deposits. Green-colored pseudohexagonal plates of Mg-chlorite occur in cavities of the magnetite skarn at the Kamaishi mine, Iwate Prefecture. Light-brown aggregates of scaly Mg-chlorite (manganoan leuchtenbergite) have been reported from a metamorphosed manganese deposit in crystalline schist at Muramatsu, Nagasaki Prefecture. The polytype of both minerals is IIb (Shirozu, 1958a, 1961).

7.3. Fe- A N D FeMg-CHLORITES OF HYDROTHERMAL METALLIC ORE VEINS

Fe-chlorites and FeMg-chlorites occur as important constituents of various metallic ore veins which are genetically related to Paleogene-Neogene volcanism and are regarded as being of a subvolcanic hydrothermal type. The chlorites are especially abundant in Cu-ore veins. A mineralogical study of these chlorites was first made by Sudo (1941, 1954), who identified a dark green chlorite from the Arakawa mine as chamosite and two chlorites from the Ani mine as thuringite and chamosite on the basis of chemical, X-ray and DTA studies. Subsequent investigations by Abe (1957), Shirozu (1958a, 1961, 1963), Nakamura (1960, 1963), Nagasawa (1961), Nagasawa et al. (1976), etc. have revealed that the chlorites in the ore veins are rich in Fey ranging from Fechlorite to FeMg-chlorite, and that the polytype of the Fe-chlorites is mostly Ib (P = 90"), often accompanied by Ib (P = 97") or IIb, while the majority of the FeMg-chlorites is 116. Table 7.2 lists X-ray powder data for the Fe-chlorites. These minerals are closely related chemically to berthierine, which is common in iron formations of the world and has a kaolin-type structure. However, the Fe-rich minerals so far identified in Japan have a chlorite structure. Data for chemical analyses of the Fe-chlorites in certain ore veins are given

248

CHLORITE MINERNLS

TABLE 7.2. X-Ray powder data for Fe-chlorites in metallic oreveins (114.6 mm diameter camera, FeKa radiation)

1)

hkl 001 002 003 020 004 005 20i, 200 202 201

14.1 7.04

001 002 Oo3 020 004 005 200,201

}

2) 4 10

Oo7

1

14.1 7.05

5 10

4.69

4

4.70

4

4.69

5

10 3

3.53 2.83 2.68

9 2 3

3.52 2.83 2.67

9 4 1

2.61 2.57

3 2 3 3

5

2 3 3

2.52 2.45

2.51

2.46 2.40 2.28

2.40*

1/2*

2.14

4

2.08

1I2

2.01

5

2.02

2

1.892 1.831

2 1

204 205 007 204 206 205

4 10

3.52 2.82

202 203 202 204

14.1 7.05

3)

2.15 2.07 2.02

1 1 1

206 1.762 1 1.776 4 207 1.721 1 1.716 1 1.668 2 206 208 4 1.568 060 1.559 060 5 1.558 5 1.559 5 062 1.523 062 2 1.520 3 1.523 3 -1) IIb Fe-chlorite from the Taishu mine, Nagasaki Prefecture (Shirozu, unpublished data). 2) IIb 16 (/I = 97") Fe-chlorite from the Myoho mine, Wakayama Prefecture (Shirozu, unpublished data). 3) Ib (B = 90") Fe-chlorite from the Sayama mine, Akita Prefecture (Shirozu, 1958a). *Probably due to Ia structure formed by grinding.

+

in Table 7.3, Nos. 1-3. The chemical compositions of the chlorites in the ore veins, as obtained by X-ray measurements of the cell dimensions and by chemical analysis, are shown in Fig. 7.2 along with the polytypes and regions of occurrence (Nagasawa et al., 1976). The figure indicates that the variations in Fe and Mg content are wide, excluding the Fe-poor part. The tetrahedral A1 vs. octahedral Fe relation shows the same trend as that of the chlorites in schists and serpentinites mentioned above. It is of interest to note, however, that the amount of tetrahedral A1 in the FeMg-chlorites of ore veins appears to be slightly less than that in the FeMg-chlorites of schists having an identical Fe/ (Fe Mg) ratio. Fig. 7.2 also demonstrates that FeMg-chlorites are found in epithermal veins of the Green Tuff regions, but most of the Fe-chlorites occur in so-called xenothermal veins outside the Green Tuff regions. Nagasawa et al.

+

Fe- AND FeMg-CHLORITES O F ORE VEINS

239

TABLE 7.3. Chemical analysis of Fe-chlorites in nietallic ore veins and FeMg-chlorites in tufficeous sediments

Total

_

_

~

21.34% 0.21 20.73 5.20 40.17 0.89 0.99 0.04

23.38% 19.32 2.51 38.38 0.58 5.39 tr

22.81 %

10.66 0.16

10.62 0.48

10.80 0.23

100.39

100.66

100.67

-

20.35 4.84 34.87 0.56 6.11 0.10

29.45 % 0.20 20 04 4.08 18.69 0.36 14.93 0.95 0.42 0.22 9.82 0.84 (lOO.00)

30.84'%, 0.12 14.15 2.59 18.42 0.10 20.62 0.59 0.21 0.04 10.82 0.88 99.38 ~-

No. of cations on the basis of 14 oxygens ~~

Tetr.

Si A1

2.462 1.538

2.633 1.367

2.537 1.463

2.967 1.033

3.154 0.846

Al Ti

1.280 0.018 0.452 3.874 0.087 0.170 0.005

1.196

1.204 0.405 3.242 0.053 1.012 0.012

1.346 0.015 0.309 1.575 0.031 2.242 0.102 0.082 0.028 5.730

0.860 0.009 0.199 1.575 0 008 3.143 0.065 0.042 0.005

Fe3+

Oct.

Fez+ Mn Mg Ca Na

-

0.212 3.612 0.056 0.904

-

K Total

5.886

5.980

5.928

5.906

1) Fe-chlorite from the Ashio mine, Tochigi Prefecture (Nakamura, 1960). 2) Fe-chlorite from the Kishu mine, Mie Prefecture (Shirozu, 1958a). 3) Fe-chlorite from the Sayama mine, Akita Prefecture (Shirozu, 1958a). 4) FeMg-chlorite in tuffaceous sandstone, Yamanaka, Ishikawa Prefecture (Kimbara and Sudo, 1973). The analysis is corrected for quartz and feldspar impurities. 5 ) FeMg-chlorite in tuff breccia, Taiheizan, Akita Prefecture (Kimbara et al., 1973; Kimbara, 1975).

(1976) have ascribed this difference to a possible difference in FejMg ratio in the environment of crystallization of the chlorites. The chlorites in the ore veins are usually associated with quartz and sulfide minerals such as chalcopyrite, pyrite, etc., and occasionally with hematite, kaolinite, calcite, dolomite, etc. They occur as hemispherical to subparallel aggregates of dark green scales and also as massive or powdery aggregates of minute scales. The former mineral is mostly Ib (p = 90') Fe-chlorite, and the latter tends to be ITb FeMg-chlorite or mixtures of two polytypes, i.e. Ib (/3 = 90") plus Ib (p = 97"), or Ib (p = 90") plus IIb (Fig. 7.2). Some Ib (p = 90") chlorites occurring in loose aggregates of powdery scales readily transform to the

250

CHLORlTE MINERALS 1.(

A B A A

Ib(90')

m

Ib(903+Ib(973

0 Q Ib(90')+IIb

0 IIb

Fig. 7.2. Chemical compositions of chlorites in hydrothermal metallic ore veins (Nagasawa et al., 1976). A, From veins outside the Green Tuff region; B, from veins in the Green Tuff region.

I n or Ib (p = 97") structure on grinding, as a result of shifting of the 2:l layer relative to the interlayer sheet (Shirozu, 1963). In the case of the mixtures of two polytypes, the compositions plotted in Fig. 7.2 are regarded as averages, and further analysis is required. A material composed of coarse scales of Ib (p = 90") and IIb chlorites from the Osarjzawa mine (Shirozu, 1958a) has been shown to consist of a subparallel intergrowth of Ib (j3 = 90") FeMg-chlorite with Fe/(Fe Mg) = 0.65 and IIb FeMg-chlorite with Fe/ (Fe Mg) = 0.50 (Shirozu, 1961), for which the respective compositions are joined by a line in Fig. 7.2. Under crossed nicols, the former chlorite shows the normal interference color of grayish yellow but the latter has an abnormal reddish purple color. It should be noted also that the tetrahedral A1 content is slightly less in the former, unlike the general trend for chlorites. The crystal structure of Ib ( P = 9W) Fe-chlorite from the Tazawa mine, Akita Prefecture, has been refined by Shirozu and Bailey (1966). The results indicated that the tetrahedral network is distorted by 5" tetrahedral rotatjons in a direction which gives rise to a favorable hydrogen bond system between the 2:l layer and the interlayer sheet. This direction is in an opposite sense, relative to the 2:l octahedral cations, to that found in most layer silicates. Of the octahedral Fe,

+

+

FERROMAGNESIAN CHLORITES IN TUFFS

25 1

60 % is concentrated in the 2: 1 layer, which suggests that most of the octahedral A1 is contained in the interlayer sheet. 7.4. FERROMAGNESTAN CHLORITE MINERALS IN MIOCENE TUFFACEOUS SEDIMENTS

Miocene formations composed mainly of pyroclastic sediments are extensively distributed on the Japan Sea side of the Japanese Islands. They are called “Green Tuff” due to the characteristic greenish color which arises from their green minerals. Recent studies on the clay mineralogy of these fine-grained green minerals have revealed that they are composed mainly of chlorites, interstratified chlorite/saponites and saponites. All are chemically ferromagnesian, and the interstratified minerals predominate. Metallic ore veins and Kuroko deposits are distributed in the Green Tuff regions, accompanied by various chlorite minerals. The FeMg-cblorites in the ore veins have been described above, and the magnesian chlorite clay minerals and sudoites occurring in the alteration zones of Kuroko deposits will be described below. The chlorite minerals discussed in this section are considered to have formed regionally in the tuffaceous sediments, together with zeolites, as a result of diagenetic alteration with no direct relation to the ore deposits. Kimbara and Sudo (1973) have described chloritic clay minerals from Miocene tuffaceous sandstone in the Yamanaka district, Tshikawa Prefecture. They divided the tuffaceous formation into the following four zones on the basis of the nature of the chloritic minerals : (1) interstratified chlorite/saponite zone (corrensite zone), (2) interstratified chlorite/saponite-chlorite zone (transitional zone), (3) swelling chlorite zone, and (4) chlorite zone. The name “swelling chlorite” is used here to indicate a chlorite-like mineral showing a slight expansion on ethylene glycol solvation. The 14.3 A reflection of swelling chlorite expands to 14.6 8, on such solvation. The powder pattern (Table 7.4, No. 1) agrees with that of the IIb polytype, although the intensity of the 14 A reflection is stronger than that of the 7 A. These data suggest that the mineral is an interstratified FeMg-chlorite/saponite having a small amount of saponite layers similar to some of the minerals presented in section 7.5. Chlorite from the chlorite zone shows the character of FeMg-chlorite. The chemical analysis is given in Table 7.3, No. 4. The powder data (Table 7.4, No. 2) indicate that the Ib (p = 97”) polytype is present in addition to Ilb. Kimbara et al. (1973) and Kimbara (1975) have reported an FeMg-chlorite with unusual properties from Taiheizan, Akita Prefecture. It occurs in amygdales of andesitic tuff breccia in close association with interstratified chlorite/ saponite. The X-ray pattern (Table 7.4, No. 3) indicates IIb FeMg-chlorite, and no apparent changes are observed on solvation and NH4 saturation despite the

CHLORITE MINERALS

252

TABLE 7.4. X-Ray powder data for ferromagnesian chlorite minerals in tuffaceous sediments (diffractometer, CuKa radiation) 1)

2)

3)

Untreated hkl 001 002 003 02,ll 004 005 20i 202 201 203 202 204 205 204 206 205 20i 206 208 060 062

d(& 14.34 7.123 4.741 4.618 3.553 2.832

Z 100 89 24 9 46 17

2.596 2.559 2.453 2.391 2.269 2.025 2.009 1.888 1.831

16 19 16 14 10

1.667 1.567 1.544 1.511

6 11 16 6

5

16 7 5

d(h 14.45 7.142 4.745 4.629 3.551 2.841 2.666 2.601 2.558 2.453 2.395 2.268 2.029 2.009 1.887 1.827 1.711 1.664 1.566 1.547 1.510

Z 85 100 30 10 52 11 6 7 9 13 8 6 5 10 3 4 6 5 10 15 8

After 450°C

d(& 14.49 7.197 4.786 4.637 3.588 2.872

Z

d(&

Z

170 150 47 4 55 10

14.27 7.197 4.769

40 50 29

3.577 2.870

24 6

2.592 2.551 2.458 2.397 2.282 2.052 2.019

3 3 4 2 2 3 2

2.439

2

2.042 2.009

2 2

1.578 1.545 1.511

2 5 2

1.584 1.534

1 2

1.418 7 7 1.417 1.431 2 1.431 Oo1OI 064 208 1.396 9 1.394 8 1.406 2 1.404 2 1) IIb ferromagnesian "swelling chlorite" from tuffaceous sandstone, Yamanaka, Ishikawa Pref. (Kimbara and Sudo, 1973). 2) TI6 Ib (/3 = 97") FeMg-chlorite from tuffaceous sandstone, Yamanaka, Ishikawa Prefecture (Kimbara and Sudo, 1973). 3) IIb FeMg-chlorite in tuff breccia, Taiheizan, Akita Prefecture (Kimbara et al. 1973).

+

fact that a small amount of interlayer water is detected from DTA curves. The chemical composition (Table 7.3, No. 5 ) is close to that of diabantite, which is characterized by a small amount of tetrahedral Al. The CEC value at pH 7 is 16.1 meq/100. The exchangeable cations are as follows: Ca, 10.5; Mg, 3.2; Nay 1.6; K, 0.8 meq/100g. The heat stability curve of the mineral recorded with a high temperature diffractometer indicates a slow decrease in the 14 A basal spacing in the temperature range from about 400 to 700°C. This contrasts with the curves for usual chlorite, vermiculite, saponite or interstratified chlorite/ saponite, recorded for comparison. Kimbara et a/. (1973) have obtained a DTA curve showing a vermiculite-like peak system above 500" C, and concluded that the mineral is a highly chloritic vermiculite with a small proportion of imperfect hydroxy interlayer. It is of interest that the basal reflections after heating at

MAGNESIAN CHLORITE MINERALS IN KUROKO DEPOSITS

253

450°C for 1 hr (Table 7.4, No. 3) can be explained by a random interstratification of the 14.33 A chlorite layer with a small amount of 9.5 A dehydrated layer as in the case of interstratified Mg-chlorite/saponites from Kuroko deposits (cf. Fig. 7.3). Kohyama et al. (1975) have reported an FeMg-chlorite rather rich in Fe from Oya, Tochigi Prefecture. It occurs as a constituent of clayey rock fragments in a rhyolitic tuff, closely associated with a randomly interstratified chlorite/smectite, smectite, celadonite, analcime and quartz. X-ray, chemical and thermal investigations have been made on material containing some impurities. The polytype shown by the powder pattern is Ib (P = 90"). Kohyama et al. concluded that this mineral is an FeMg-chlorite having abnormal structural water, of which a considerable part is expelled below 250°C. 7.5. MAGNESIAN CHLORITE MINERALS IN ALTERED WALL ROCKS OF KUROKO DEPOSITS

In the altered wall rocks of Kuroko deposits of the Green Tuff regions, various chlorite clay minerals occur (see Chapter 3). Of these minerals, magnesian chlorite minerals poor in Fe are the most common, and a large number of studies have been made on them. The first mineralogical study was that on a clay associated with the Kuroko deposit at Udo, Shimane Prefecture, by Takahashi and Yagi (1930). They undertook chemical and TG analyses and concluded that the mineral was a chlorite close to clinochlore or pseudophyte. They also noticed its rather small A1 content and property of being gelatinized in water. This mineral is now inferred to be an interstratified Mg-chlorite/saponite. The clay mineralogical investigations initiated by Sudo (1954) and continued by Sakamoto and Sudo (1956), Iwao and Minato (1959), Osada and Sudo (1961) and Hayashi (196 l), revealed the common occurrence of Mg-chlorite (leuchtenbergite) in many Kuroko deposits, particularly in Kuroko-type gypsum deposits. In some of these studies, long spacing X-ray reflections (about 30 A) were recorded. They were attlibuted to the existence of a regularly interstratified mineral composed of chlorite and smectite. Sugiura (1962) also confirmed the existence of a regularly interstratified mineral at the Noto gypsum mine, Ishikawa Prefecture, and described it as an interstratified chlorite/vermiculite. Shimoda (1970) investigated a chlorite mineral from the Hanaoka mine, Akita Prefecture, and referred to it as an expandable chlorite-like mineral. Recently, Shirozu et al. (1975) have made extensive studies of the magnesian chlorite minerals of some Kuroko deposits, and revealed the occurrence of irregularly interstratified Mg-chlorite/saponite having small amounts of saponite layers in addition to the Mg-chlorite and 1 :1 regularly interstratified Mg-chlorite/saponite. They also described some of the general characteristics of the Kuroko Mg-

254

CHLORITE MINERALS

chlorite minerals. The following account is based mainly on this study, and also gives appropriate consideration to the interstratified minerals. 7.5.1. Modes of occurrence The magnesian chlorite clay minerals occur in the intensely argillized zone (“clay zone”) which is distributed within and immediately surrounding the Kuroko deposits. The clay minerals found most abundantly in this zone consist of sericite. The magnesian chlorite minerals are second most widespread, but predominate in gypsum deposits. Pyrite is usually associated with the magnesian chlorite minerals, but quartz is rare. The magnesian chlorite clays are fine-grained, grayish white in color, occasionally with a greenish tint, often exhibiting a waxy luster, and are generally not distinguishable from sericite clays with the naked eye. Under the microscope, they usually appear as aggregates of 1 to 10 p-size flakes, and have a feathery appearance. In typical Kuroko deposits, the Mg-chlorites commonly occur within the deposits or in the intercalated clays, and the interstratified Mg-chlorite/saponites are mainly found in the hanging-wall clay. However, in the gypsum deposits of the Wanibuchi mine, Shimane Prefecture, the interstratified minerals as well as Mg-chlorites occur abundantly within the deposits, and a close association between the interstratified minerals and talc is seen. 7.5.2. X-ray patterns and interstratiJed structures Mg-chlorites from the Kuroko deposits yield four X-ray basal reflections of approximately equal intensities from relatively small basal spacings (14.1414.25 A). Minerals showing apparently larger basal spacings are usually interstratified minerals, as discussed below. The polytype of the Mg-chlorites is usually IIb, but Ja is occasionally found (Table 7.5, Nos. 1 and 2). The b dimensions measured on the 060 reflection range from 9.18 A to 9.215 A, and are thus smaller than those of normal well-crystallized Mg-chlorites (9.21-9.22 A). The interstratified Mg-chlorite/saponites give relatively strong 14 A reflections compared with Mg-chlorites, and with increase in the amount of saponite layers, the 14 A reflection intensity increases with accompanying long-spacing (about 30 A) and additional basal reflections. Simultaneously with this, the line profiles are broadened, but the basal reflections corresponding to those of usual chlorite maintain an approximately integral sequence of relatively large spacings (14.3-14.6 A). lnterstratification with expandable layers is revealed by solvation, K-saturation and heat treatment, and it is concluded that an irregularly interstratified Mg-chlorite/saponite having small amounts of saponite layers, and a 1:1 regularly interstratified Mg-chlorite/saponite constitute the main constituents of these interstratified minerals (Shirozu et al., 1975). In addition, it has been suggested that there should be an approximately 3:l regu-

MAGNESIAN CHLORITE MINERALS IN KUROKO DEPOSITS

255

TABLE 7.5. X-Ray powder data for magnesian chlorite minerals from Kuroko deposits (diffractorneter,CuKa radiation) 3)

After 500°C

2O0C

hkl 001 002 003 020 004

005 200 202 201 203 202 204 204 206 205 207 206 208 060 062

d(& 14.3 7.14 4.74 4.58 3.553 2.846

Z _ _

2.583 2.544 2.443 2.390 2.258 2.009 1.885

10 15 15 5

35 65 40 15 55 15

5

.

d .( h,

14.3 7.12 4.74 4.58 3.55 2.846 2.638 2.576 2.538 2.434 2.378 2.256 2.003 1.879 1.823 1.723 1.664 1.566 1.534 1.500

Z 81 100 63 20 82 20 20 18 25 21 45 13 32 7 7 6 14 16 41 10

}

d(&

Z

d(&

Z

14.8 7.325 4.844 4.572 3.590 2.882 2.635

47 28 32 65 30 10 20

2.547

40

2.409

30B*

14.2 7.577 4.795 4.595 3.520 2.900 2.650 2.579 2.548 2.447

40 10 12 50 20 10 25 28 25 23

2.268 7 2.268 8 2.009 14B* 2.013 7B 3 1.897 4 1.895 1.810 2 5B 1.726 1.730 1.682 1.568 10 1.564 6B* 15 1.536 1.534 36 1.536 28 10 1.504 1.500 8 1.507 8 1) IIb Mg-chlorite from the Wanibuchi mine, Shimane Prefecture (Sakarnoto and Sudo, 1956). 2) Ia 1Ib Mg-chlorite from the Wanibuchi mine, Shirnane Prefecture (Katsumoto and Shirozu, unpublished data). 3) Expandable chlorite-like mineral from the Tsutsumizawa deposit, Hanaoka mine, Akita Prefecture (Shimoda, 1970). *B = Broad reflection. 20 10

}

+

larly interstratified chlorite/saponite structure which gives about a 20 A reflection, as seen in the pattern in Fig. 7.3 A (Watanabe et al., 1974). Adoption of the name of saponite (trioctahedral smectite) for the expandable component is based on the results of glycerol liquid solvation after Mg-saturation (17.8 A) and of K-saturation (12.5 A). However, the heating effects are vermiculitic rather than smectitic. Materials heated at 500°C for 1 hr give ca. 14 A reflections with only slightly decreased d-spacings (Fig. 7.3j, and rehydrate gradually; similar changes are observed on heating at 300 or 400°C, but in these cases rehydration occurs very rapidly. In this respect, Sugiura (1962) termed a 1:1 regularly interstratified mineral from the Noto mine a chlorite/vermiculite mixed layer mineral. Shimoda (1970) has described “an expandable chlorite-Iike mineral”, the Xray data and chemical analysis for which are included in Table 7.5, No. 3 and

CHLORITE MINERALS

256

14.3

B

I

14.3A - 1,:

1,2

3:

9.5A ' 1 I 2 ,A 2" 10" 20" 28

I

I

41 I

15 3

l

30'

Fig. 7.3. X-ray diffraction diagrams of an irregularly interstratified Mg-chlorite/saponite having a small amount of saponite layers (from the Iwami mine, Shimane Prefecture; oriented aggregates) (Shirozu et al., 1975). A, Untreated material; B, material heated at 500°C for 1 hr.

Table 7.6, No. 5, respectively. He noticed a similarity between the mineral and swelling chlorite or corrensite, and deduced it to be an interstratification of chlorite and swelling chlorite. concluding that :he specimen may be defined as a chlorite-like complex of saponite with magnesium hydroxide, formed in the process of hydrothermal alteration. According to Shirozu et al. (1975), however, the patterns of heated specimens of these minerals can be explained on the basis of random interstratification of chlorite with small amounts of dehydrated 9.5 A layers as shown in Fig. 7.3 by visual inspection, so that it is not necessary to introduce swelling chlorite as an expandable component. They have applied the structure model of swelling chlorite proposed by Honeyborne (1951) and Martin Vivaldi and MacEwan (1960) to the whole interstratified chlorite/saponite structure. That is to say, the interlayer hydroxide sheets of the chlorite layers are considered to be discontinuous laterally. and to be partially replaced by cation-water packets or sheets of saponite layers which show rapid rehydration or resistance to collapse on heating. In the case of insufficient development of cation-water packets, the

257

MAGNESIAN CHLORITE MINERALS IN KUROKO DEPOSITS TABLE 7.6. Chemical analysis of magnesian chlorite minerals from Kuroko deposits 1) 2) 3) 4) 25.05 % 28.97 % 29.07 % 30.38 % 0.32 0.32 35.53 21.82 26.59 24.21 0.83 0.48 2.90 0.11 0.80 3.67 3.62 2.34 0.05 0.20 0.13 29.90 23.46 25.17 26.31 0.15 0.15 0.19 0.02 0.08 tr 0.29 0.44 0.15 tr 0.08 0.23 10.76 11.40 13.31 12.72 2.76 0.80 1.93 0.64

5) 32.72 % 0.03 20.28 1 .oo

-

0.06 24.47 1.97 0.25 tr 12.57 7.02

6) 34.33 %

-

14.94 0.15 0.63 0.04 32.19 0.33 0.11 0.20 13.18 3.67

99.32 100.37 99.77 100.69 99.08 99.24 Total Mg-chlorite from the Yunosawa deposit, Furutobe mine, Akita Prefecture (Shirozu et al., 1975). Mg-chlorite from the Matsumine deposit, Hanaoka mine, Akita Prefecture (Shirozu et al., 1975). Mg-chlorite from the Wanibuchi mine, Shimane Prefecture (Sakamoto and Sudo, 1956). Interstratified Mg-chlorite/saponite from the Iwami mine, Shimane Prefecture (Shirozu et al., 1975). 5 ) Expandable chlorite-like mineral from the Tsutsumizawa deposit, Hanaoka mine, Akita Prefecture (Shimoda, 1970). 6) Interstratified Mg-chloritelsaponite from the Wanibuchi mine, Shimane Prefecture (Shirozu et aL, 1975).

1) 2) 3) 4)

saponite component would not form expandable layers, as recognized in some samples. These give a faint endothermic peak which can be attributed to the removal of interlayer water associated with interlayer cations at 205-210" C on the micro-DTA curve, but show the X-ray behavior of non-interstratified minerals. Another model has been proposed by Nagasawa and Tsuzuki (1974) for the chloritelsmectite interstratified structure. In this model, excess negative charges which may be effective in resistance to collapse, are created on the interlayer surface of 2:l layers in the expandable layers, assuming all the tetrahedral compositions to be similar throughout the whole interstratified structure. 7.5.3. Chemical composition

Chemical analysis of Mg-chlorites and interstratified Mg-chlorite/saponites from Kuroko deposits has shown that the major cations are Mg, A1 and Si, with some variation in the relative contents. Some of the analytical results are given in Table 7.6. The minerals are poor in Fe and in other minor components, and the compositions can be expressed by an Si-Al-R diagram (R = total other cations; mainly Mg) as shown in Fig. 7.4, which incorporates all the available data for magnesian chlorite clay minerals from Kuroko deposits (Shirozu et al., 1975). Some of the data given as interstratified chlorite/saponite were originally described as chlorite (Nos. 12, 13 and 16). However, Shirozu et al. state that

258

CHLORITE MINERALS

Fig. 7.4. Chemical compositions of magnesian chlorite minerals from Kuroko deposits (Shirozu et al., 1975). Solid circles: Mg-chlorite. Open circles: interstratified Mg-chlorite/saponite. 1,2,8) From the Furutobe mine, Akita Prefecture. 3) From the Matsumine deposit, Hanaoka mine, Akita Prefecture. 4,5,7,9) From the Wanibuchi mine, Shimane Prefecture. 6) From the Iwami mine, Shimane Prefecture (1-9, Shirozu et a/.,1975). 10, 12) from the Hanaoka mine, Akita Prefecture (Hayashi, 1961). l l) From the Wanibuchi mine, Shimane Prefecture (Sakamoto and Sudo, 1956). 13) From the Wanibuchi mine, Shimane Prefecture (Iwao and Minato, 1959). 14) “Expandablechlorite-like mineral’’ from the Hanaoka mine, Akita Prefecture (Shimoda, 1970). 15) Chlorite/vermiculite mixed layer mineral, from the Noto mine, Ishikawa Prefecture (Sugiura, 1962). 16) From Udo, Shimane Prefecture (Takahashi and Yagi, 1930).

distinct properties of interstratified structure are identifiable in the descriptions, viz. the relatively large intensity of the 14 A reflection, changes in the X-ray patterns after solvation and/or heating, considerable dehydration at low temperatures, etc. The diagram indicates that a definite difference exists in the chemical composition, particularly the Si amount, between the Mg-chlorites and interstratified Mg-chlorite/saponites, and that their compositions do not represent orthochlorite. It is also apparent that the minerals from typical Kuroko deposits rich in sulfide metal ores in the Hokuroku district (Nos. 1, 2, 3, 8, 10, 12 and 14) have more A1 and less Mg than those from Kuroko-type gypsum deposits of other localities (Nos. 4, 5, 7, 9, 11, 13 and 15). As to minor components, Shirozu et al. (1975) have pointed out that the interstratified minerals have relatively low Fe contents (Fe oxides, 1-2.5%) compared to those of the chlorites (Fe oxides, 3-573. However, no reasonable explanation for this difference has yet been found. In contrast to the Fe contents, there are no significant differences in lime or alkali contents between the two groups of minerals. This suggests that very small or small amounts of these cations are contained in or adsorbed by the chlorite lattices. The structural formulae of some Mg-chlorites from the Kuroko deposits evaluated by Shirozu et al. (1975) indicate that the octahedral sheet contains some vacancies due to substitution of 2A1 for 3Mg. This may be related to the fact that the Mg-chlorites fall in the area of lower R than the orthochlorite line

DIOCTAHEDRAL CHLORITE MINERALS

259

in the Si-A1-R diagram, together with the interstratified Mg-chlorite/saponites. In this respect, the Kuroko Mg-chlorite may belong to the category of leptochlorite proposed by Tschermak. The interstratified Mg-chlorite/saponite may also be regarded chemically as a kind of leptochlorite. In addition to these chemical characteristics, the Kuroko Mg-chlorite differs from well-crystallized Mg-chlorites of other origins in its b dimension, in the relations of d(OO1) or the infrared OH bands to the tetrahedral composition, etc., as discussed by Shirozu et al. (1975). They have suggested that the Kuroko Mg-chlorite contains some A1 in the 2:l octahedral sheet, which may contrast with the character of usual well-crystallized trioctahedral chlorite.

7.6. DIOCTAHEDRAL CHLORITE MINERALS

Dioctahedral chlorites have a dioctahedral 2:l layer and a dioctahedral or trioctahedral interlayer sheet. Sudo et al. (1954) first inferred the existence of dioctahedral chlorite as a component of an interstratified mineral from a pyrophyllite deposit of the Kurata mine, Yamaguchi Prefecture. Since then, the occurrence of dioctahedral chlorite as a single mineral has been reported from a number of places in the world, and the mineral was named sudoite. At present this name is applied to a mineral having a trioctahedral interlayer sheet and some Mg. In Japan, dioctahedral chlorites have been found in the altered wall rocks of a large number of Kuroko deposits and in several pyrophyllite deposits. Both deposits are of hydrothermal origin. Mineralogical descriptions of sudoites associated with Kuroko deposits were given first for materials from the Kamikita mine, Aomori Prefecture, by Hayashi and Oinuma (1964) and from the Furutobe mine, Akita Prefecture, by Tsukahara (1964). Recent descriptions have also been given by Shirozu et al. (1971), Kimbara and Nagata (1974), Shimoda (1975), Tsuzuki and Honda (1975), and Honda (1975). The results of these studies indicate that the minerals from Kuroko deposits are rich in A1 but contain considerable amounts of Mg. Sudo and Sat0 (1966) and Shirozu and Higashi (1976) have undertaken X-ray studies, mainly on the nature of the octahedral sheets of sudoites. Henmi and Yamamoto (1965) and Henmi et al. (1966) have reported the occurrence of various dioctahedral chlorites which are very poor in Mg, from several pyrophyllite deposits in the Itaya-Mitsuishi district, Okayama Prefecture, and its vicinity. Fujii et al. (1971) have described a sudoite from the pyrophyllite deposit of the Shinyo mine, Nagano Prefecture. Dioctahedral chlorite frequently forms a 1 :1 regularly interstratified mineral with montmorillonite. This is called tosudite. A regularly interstratified mineral with dioctahedral mica is also known. These minerals are described in Chapter 8.

CHLORITE MINERALS

260

7.6.1. Sudoites fi’om Kuroko deposits Following the descriptions of Hayashi and Oinuma (1964) and Tsukahara (1964), sudoite has been identified in a large number of Kuroko deposits and is regarded at present as a rather common mineral of the altered wall rocks of the deposits. It occurs as fine-grained, white to pale gray aggregates, usually in close association with sericite and occasionally with kaolinite, Mg-chlorite, etc. In the Honko deposit of the Kamikita mine, sudoite is found together with an interstratified mica/montmorillonite in the alteration zone composed of pyrophyllite, kaolinite, diaspore, quartz and barite. Kimbara and Nagata (1974) have reported that sudoite and tosudite occur abundantly around a Kuroko deposit located at Niida, Akita Prefecture. The X-ray patterns of sudoites show a relatively strong 003 reflection. The d (001) spacings reported in the literature range from 14.16 to 14.29 A, but are mostly 14.16 to 14.20 A. The d(060) values are invariable: 1.508 to 1.509 A. The only polytype so far known from powder patterns is IIb (Table 7.7, Nos. 1 and 2). TABLE 7.7. X-Ray powder data for dioctahedral chlorites (diffractometer, CuKa radiation) 1)

2)

Z

hkl

62 60 122 40 74 22 10 50 26 10 12 12 25 8 10 7

3)

Z

d(A) 14.5 7.22 4.74 4.46 3.556 2.860 2.561 2.503

1

14.72 100 84 002 7.190 49 26 003 4.766 100 100 020 4.525 20 52 004 3.573 52 34 005 2.846 18 20 202 2.533 9 32 201 2.506 20 32 2.409 10 20 3 202 2.354 6 2.325 26 204 2.231 5 2.197 4 007 2.026 9 2.028 16 204 1.984 15 1.970 14 206 1.872 4 205 1.809 7 207 1.705 3 1.688 4 206 1.633 3 1.646 20 208 1.556 14 1.557 9 1.536 4 060 1.509 8 1.509 8 1.489 34 062 1.433 8 1.474 2 _ _ ~ 1) Ilb sudoite from the Honko deposit, Kamikita mine, Aomori Prefecture (Hayashi and Oinuma, 1964). Reflections due to impurities are omitted. 2) IIh sudoite from a Kuroko deposit located at Niida, Odate, Akita Prefecture (Kimbara and Nagata, 1974). 3) Ja dioctahedral chlorite from a pyrophyllite deposit located at Itaya, Okayama Prefecture (Henmi and Yamamoto, 1965). Reflections due to impurities are omitted. 001

14.2 7.14 4.72 4.49 3.54 2.84 2.54 2.50 2.40 2.34 2.23 2.03 1.98 1.866 1.817 1.698

d(&

DIOCTAHEDRAL CHLORITE MINERALS

261

The X-ray reflections are usually stable on heating up to about 500" C, and on solvation. However, the sudoite from the Honko deposit of the Kamikita mine described by Hayashi and Oinuma (1964) shows a slight decrease on heating at 450" C for 1 hr, and a slight increase on ethylene glycol solvation, in the d spacings of most basal reflections. The sudoite from the Furutobe mine described by Tsukahara (1964) shows a slight decrease in the d spacings of the main basal reflections except the 7 A reflection on heating at 510°C for 1 hr. There is no remarkable change in the 14 A reflection on solvation. These data suggest the existence of interstratifications of sudoite with small or very small amounts of expandable layers. Chemical analysis of sudoites almost free from or with minimal impurities (Table 7.8, Nos. 1-5) have shown that they contain large amounts of A1 and small amounts of Mg. Fe, Ca and alkalis are generally very sparse. The numbers of main cations evaluated on the basis of OI,,(OH)~from the analyses after exclusion of the major impurities are: tetrahedral Si, 3.0-3.3; tetrahedral Al, 0.7-1.0; octahedral Al, 3.0-3.3; octahedral Mg,1.2-1.8. The total numbers of octahedra1 cations including minor components are 4.6 to 4.9, which is a little TABLE 7.8. Chemical analysis of dioctahedral chlorites

SiOz Ti02 Ah03 Fez03 FeO MnO MgO CaO NazO KzO Liz0 HzO(+) HzO(-) Total

1) 33.10% 0.30 37.43 0.87 tr tr 13.12 tr 0.15 0.29 13.32 2.1 1 Pzos 100.69

2) 35.67% 0.19 37.41 0.20 0.09 0.02 11.97 0.66 0.16 0.43 13.30 0.88 0.01 100.99

3) 34.36% 38.84 0.49

-

4) 39.01% 0.47 32.15 0.90 0.10

-

10.14 0.54 0.10 1.52 -

10.21 0.07 0.66 0.12

13.98 0.84 99.57

-

14.15 S 0.42 99.50

5) 35.63% none 34.87 5.01 0.43 0.05 8.63 1.13 0.24 0.46 12.24 1.91 Pzo5 100.60

6) 43.43%

-

39.21 0.17

-

0.13 0.47 1.41 0.49 1.43 11.59 1.47 0.11 99.91

1) Sudoite from a Kuroko deposit located at Niida, Odate, Akita Prefecture (Kimbara and Nagata, 1974). 2) Sudoite from the Uchinotai deposit, Kosaka mine, Akita Prefecture (Tsuzuki and Honda, 1975). A small amount of sericite is included. 3) Sudoite from the Okunosawa deposit, Kamikita mine, Aomori Prefecture (Honda, 1975). 4) Sudoite from the Daikokuzawa deposit, Furutobe mine, Akita Prefecture (Tsukahara, 1964). Small amounts of quartz (6.3 %), illite (4.3 %) and pyrite are included. 5) Sudoite from the Honko deposit, Kamikita mine, Aomori Prefecture (Hayashi and Oinuma, 1964). A small amount of an interstratified mineral is included. 6) Dioctahedral chlorite from a pyrophyllite deposit located at Itaya, Okayama Prefecture (Henmi er al., 1965). Small amounts of kaolin and pyrophyllite are included.

262

CHLORITE MINERALS

less than the 5.0 corresponding to a chlorite with one dioctahedral sheet and one trioctahedral sheet. Sudo and Sat0 (1966) have investigated the cation populations in the two octahedral sheets of sudoite specimens obtained from the Kamikita mine using powder reflections. They concluded that the intensities of the reflections correspond to a model intermediate between a structure with a 2:l dioctahedral sheet and an interlayer trioctahedral sheet and a structure with two dioctahedral sheets. Recently, Shirozu and Higashi (1976) have refined the z-parameters of the atomic planes and the octahedral cation populations in two sudoites (one from the Matsumine deposit of the Hanaoka mine, Akita Prefecture, and the other from the Uchinotai deposit of the Kosaka mine, Akita Prefecture) and in a regularly interstratified dioctahedral mica/sudoite, using the basal reflections. The results indicate that the interlayer O-OH space (2.80-2.84 A) is similar to, but the dioctahedral2:l layer thickness (6.53-6.57 A) is thinner than in trioctahedral chlorites, and that the octahedral cation number in the interlayer sheet is a little less than 3.0, viz. 2.6-2.8. The structural formula suggested for Kuroko sudoite is:

[Mgl.3Al~.~(OH)~l1~1f[(Mg~.~All.~)(Si3.2A1~.~)01~(OH)2l1~1In this formula the 2:l dioctahedral sheet contains a small amount of Mg, and Shirozu and Higashi (1976) have explained the lateral fit of the dioctahedral and trioctahedral sheets by the chemical composition of the two sheets. This contrasts, however, with the explanation offered by Eggleton and Bailey (1967) for the sudoite from the Tracy mine, Michigan, U.S.A. on the basis of thinning of the dioctahedral sheet and thickening of the trioctahedral sheet. 7.6.2. Dioctahedral chlorite mineralsfrom pyrophyllite deposits A large number of pyrophyllite deposits (so-called "Roseki" deposits) are distributed in southwestern and central Japan, and dioctahedral chlorite minerals are occasionally found in them. Henmi and Yamamoto (1965) and Henmi et al. (1966) have shown that the pyrophyllite deposits of Itaya, Mitsuishi and Rissho, Okayama Prefecture, and at Ebara, Hyogo Prefecture, contain dioctahedral chlorite in their high aluminous ores. The dioctahedral chlorite forms fine-grained, white aggregates with pyrophyllite, kaolin, sericite, boemite, djaspore, quartz, etc. X-ray powder date for the material with the least impurity from Itaya are given in Table 7.7, No. 3. The polytype appears to be Ia. The d(001) spacing is 14.2 A, and the d(060) spacing is 1.489 A. Changes in the X-ray pattern on heating, together with the DTA curve, indicate that the interlayer sheet of the mineral dehydroxylates at a somewhat lower temperature than Kuroko sudoite. Chemical analysis of the material from Itaya (Table 7.8, No. 6) and of a few dioctahedral chlorite-bearing materials from other localities indicates that the dioctahedral chlorites are very

REFERENCES

263

poor in Mg and contain small amounts of Li. Based on these chemical data, the chlorites may well be called donbassite or cookeite. Fuji et al. (1971) have described a dioctahedral chlorite mineral from a pyrophyllite deposit of the Shinyo mine, Nagano Prefecture. It is found in the pale brown clay which occurs as irregular masses in the deposit and is composed mainly of dioctahedral and trioctahedral chlorite minerals, sericite and quartz. The material investigated gives an X-ray pattern similar to that of sudoite, but the 001 reflection is relatively broad and is large in d-spacing and intensity. The 4060) value is 1.510 A, and the polytype shown by powder patterns is Ilb. On the basis of the changes in X-ray reflections on heating and solvation, Fujii et al. (1971) have concluded that this material consists mostly of a random interstratification of dioctahedral chlorite with small amounts (less than 20 %) of montmorillonite. However, the data appear to indicate also that a small amount of smectite may be included as a mechanical mixture in the sudoite sample rather than as an interstratified component. Based on the data so far obtained for clays of hydrothermal origin in Japan, interstratifications of dioctahedral chlorite with small to moderate amounts of' montmorillonite appear to be very sparse, despite the fact that the almost 1:l dioctahedral chlorite/montmorillonite interstratification (tosudite) frequently occurs. This situation differs rather from other cases where wide interstratifications with various proportions of components of the interstratified mineral series between dioctahedral mica and 1 :1 dioctahedral mica/montmorillonite, and also of the series between Mg-chlorite and 1:1 Mg-chlorite/saponite, commonly occur.

REFERENCES Abe, H . (1957) J . Jupan. Assoc. Miner. Petrol. Econ. Geol. 41, 192. Banno, S . (1964) J. Fac. Sci. Univ. Tokyo Sec. 11, 15, Part 3, 203. Eggleton, R. A. and Bailey, S . W. (1967) Amer. Miner. 52, 673. Fujii, N., Omori, T. and Fujinuki, T. (1971) Proc. IMA-IAGOD Mtg. 1970, IMA Vol. (Miner. SOC. Japan Spec. Pap. l), Miner. SOC.Japan, 183. Hayashi, H. (1961) J. Miner. Soc. Jupan 5 , 101. Hayashi, H. and Oinuma, K. (1964) Clay Sci. 2, 22. Henmi, K. and Yamanloto, T. (1965) Clay Sci. 2, 92. Henmi, K., Sato, Y. and Kusachi, I. (1966) Earth Sci. Rept. Okayuma Univ. 1, 63. Honda, S. (1975) 19th Ann. Mtg. Abstr., Clay Sci. SOC. Japan, 65. Honeyborne, D. B. (1951) Clay Miner. Bull. 1, 150. Horikoshi, E. (1965) J. Geol. Soc. Jupan 71,419. Iwao, S . and Minato, H. (1959) Proc. 20th Intern. Geol. Congr. Mexico, 31. Kanehira, K. (1967) Japan. J. Geol. Geograph. 38, 101. Kimbara, K. (1975) Contributions to Cluy Mineralog.y, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 42. Kimbara, K. and Nagata, H. (1974) J , Jupan. Assoc. Miner. Petrol. Econ. Geol. 69, 239. Kimbara, K. and Sudo, T. (1973) J . Japan. Assoc. Miner. Petrol. Econ. Geol. 68, 246. Kimbara, K., Shimoda, S. and Sudo, T. (1973) Cluy Miner. 10, 71.

264

CHLORITE MlNERALS

Kohyama, N., Kawabori, T. and Shimoda, S. (1975) Contributionsto Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 87. Martin Vivaldi, J. L. and MacEwan, D. M. C. (1960) Clay Miner. Bull. 4, 173. Miyashiro, A. (1957) J. Geol. SOC.Japan 63, 1. Nagasawa, K. (1961) J. Earth Sci. Nagoya Univ. 9, 129. Nagasawa, K. and Tsuzuki, Y. (1974) Clay Sci. 4, 191. Nagasawa, K., Shirozu, H. and Nakamura, T. (1976) Genesis of Vein-Type Deposits in Japan (Mining Geol. Spec. Issue 7), SOC.Mining Geol. Japan, 75. Nakamura, T. (1960) J. Miner. SOC.Japan 4, 383. Nakamura, T. (1963) J. Geosci. Osaka City Univ. 7, 97. Osada, M. and Sudo, T. (1961) Clay Sci. 1,29. Sakamoto, T. and Sudo, T. (1956) Miner. J. 1, 348. Shimane, H. and Sudo, T. (1958) Clay Miner. Bull. 3, 297. Shimoda, S. (1970) Clay Miner. 8, 352. Shimoda, S. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 92. Shirozu, H. (1958a) Miner. J. 2,209. Shirozu, H . (1958b) Miner. J. 2, 298. Shirozu, H. (1960) Mem. Fac. Sci. Kyushu Univ. D , 9, 183. Shirozu, H. (1961) Advances in Clay Science, vol. 3, p. 279, Gihodo. Shirozu, H. (1963) Miner. J. 4, 1. Shirozu, H. (1969) Sci. Rept. Dept. Geol. Kyushu Univ. 9, 105. Shirozu, H. and Bailey, S. W. (1966) Amer. Miner. 51, 1124. Shirozu, H. and Higashi, S. (1976) Miner. J. 8, 158. Shirozu, H., Ozaki, M. and Higashi, S. (1971) Clay Sci. 4, 45. Shirozu, H., Sakasegawa, T., Katsumoto, N. and Ozaki, M. (1975) Clay Sci. 4, 305. Sudo, T. (1941) J. Geol. Soc. Japan 48,423. Sudo, T. (1954) Sci. Rept. Tokyo Kyoiku Daigaku Sec. C , 3, 173. Sudo, T. and Sato, M. (1966) Proc. Intern. Clay Conf. Jerusalem 1966, 33. Sudo, T., Takahashi, H. and Matsui, H. (1954) Japan. J. Geol. Geograph. 24, 71. Sugiura, S. (1962) J. Miner. SOC. Japan 5, 311. Takahashi, J. and Yagi, T. (1930) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 4, 201, 251. Tsukahara, N. (1964) Clay Sci. 2, 56. Tsuzuki, Y. and Honda, S. (1975) 1975 Ann. Mtg. Abstr., Miner. SOC.Japan, 92. Watanabe, T., Nakamuta, Y. and Shirozu, H. (1974) J. Miner. SOC.Japan 11, Spec. Issue 1, 123

Chapter 8 Interstratified minerals

Susumu SHIMODA

In 1934, Gruner first found an interstratification of vermiculite and biotite (Gruner, 1934). Subsequently, Alexander et al. (1939), Nagelschmidt (1944), Bradley (1950), etc. reported similar minerals composed of two or more different silicate layers. The component layers of interstratified minerals resemble the minerals as they exist individually. These minerals are thus usually described in terms of the component layers, e.g. a mineral composed of mica- and montmorillonite-like layers is described as an interstratified mineral of mica and montmorillonite. If the interstratification is regular, and the nature of the component layers established, a specific name is given to the mineral, such as rectorite, tosudite, etc. In Japan, Sudo (1954) and Sudo et al. (1954a,b) first discovered and reported an interstratified mineral from the Kurata Roseki and Hanaoka Kuroko mines, respectively. The mineral has been confirmed to consist of “aluminum chlorite” and montmorillonite layers, and is known by the name tosudite. An interstratified trioctahedral chloritelsaponite was first described from a clayey vein in the Tsunemi dolomite mine by Takahashi (1959). Subsequently, minerals of this type have been found widely in alteration areas of the so-called Kuroko deposits and Kuroko-type gypsum deposits, and in some areas of the so-called Green Tuff regions. Interstratified mica/montmorillonite was first found in the Kanakura Roseki mine by Takeshi (1958). It has now been identified widely in the Roseki and Toseki deposits, in alteration areas of someKuroko deposits, and in some tuffaceous sediments. Interstratified minerals may be classified into three groups according to the manner of distribution of the component layers, viz. regular, random, and that with segregation into zones in the crystals. The direct Fourier transform method is generally used for identification of the layers (MacEwan, 1956, 1958, 1959; Dyakonov, 1961). Brindley (1956) has confirmed the interstratified structure of allevardite by means of the Fourier synthesis method. This technique is useful for determining the nature of the component layers of regularly interstratified minerals. The method given by MCring (1949), the visual inspection method, is also convenient for identifying random interstratifications. Calculations for diffraction patterns of interstratified structures were reported many years ago by Hendricks and Teller (1942), Brown and Greene-Kelly (1954), Kakinoki and Ko265

266

INTERSTRATIFIED MINERALS

mura (1952, 1954, 1962), MacEwan (1958), etc. Reynoids (1967, 1970) calculated the patterns and identified interstratified minerals. In Japan, Sat0 (1965, 1969, 1970, 1971, 1973), Sato et al. (1965), Sat0 and Kizaki (1972) calculated many diffraction patterns using Kakinoki and Komura's equation and identified numerous naturally occurring interstratified minerals. Review articles on the interstratified minerals of Japan have been given by Sudo (1959'0, 1963, 1968), and Sudo and Shimoda (1969). Thus, in the present Chapter, certain interstratified minerals of mineralogical interest are chosen, and their modes of occurrence, mineralogical properties and origin are described. 8.1.

MODES O F OCCURRENCE OF INTERSTRATIFIED MINERALS

Tn Japan, numerous interstratified minerals have been reported from various localities. Although their modes of occurrence are generally very complex, the minerals are found most commonly in alteration areas around certain kinds of hydrothermal deposits such as diaspore, pyrophyllite, pottery stone, and the so-called Kuroko deposits. In some cases they occur in geothermal areas and are occasionally found in alteration areas closely related to acidic rocks. They may also be formed by diagenetic processes without hydrothermal effects. The minerals occurring in tuffs and tuffaceous rocks associated with coal beds appear to have been transformed from montmorillonite by diagenesis without hydrothermal alteration. They also occur in the so-called Green Tuff, which is widely distributed in Japan, but some are considered to have been influenced by hydrothermal effects. Certain kinds of these minerals are found in weathered rocks, and are considered to have been formed by weathering. The occurrence and origin of the minerals are usually divided into two categories, viz. sedimentary and hydrothermal, although the natural modes of occurrence are extremely complex. The minerals found in Japan are divided here into seven groups, and the respective modes of occurrence are described. 8.1.1. Interstratijied minerals occurring in sedimentary rocks without hydrothermal alteration

During investigations of the sedimentary rocks of the coal-bearing formations of the Kamisunagawa district, Hokkaido, Kobayashi and Oinuma (1960) and Oinuma and Kobayashi (1961) located many specimens of interstratified mica/montmorillonite. The formations range in age from Cretaceous to Tertiary and the coal-bearing rocks are composed mainly of shale with some beds of tuff. The clay minerals found in the rocks are chlorite, mica, kaolinite, and interstratified mica/montmorillonites. The chlorite and mica found in the shales appear to have existed previously in the rocks, but the kaolinite is considered to have formed from chlorite by weathering. Interstratified mica/montmori~lonites

MODES OF OCCURRENCE

267

have been found in some of the tuffaceous beds and in several shales. The minerals found in the shales are considered to have been derived from mica by weathering, but the minerals found in the tuff were apparently transformed from montmorillonite by diagenesis. The former are usually associated with chlorite, mica and kaolin minerals, while the latter occur with kaolin minerals. One specimen from a tuffaceous bed of the Noborikawa Formation has been studied in detail by Sat0 et al. (1965), and a specimen from the Wakanabe Formation has been studied by Shimoda et al. (1969’0). According to Kobayashi and Oinuma (1960) and Oinuma and Kobayashi (1961), the interstratified mica/montmorillonites found in the tuff beds should be considered as alteration products of montmorillonite formed by diagenesis. Shutov et al. (1969) have reported mineralogical data for certain interstratified mica/montmorillonites formed from montmorillonite by diagenesis, and have shown a successive change in the minerals from montmorillonite to mica. However, the change in mineralogical properties from montmorillonite to mica was not fully continuous in their studies. This suggests the involvement of certain complicated conditions related to the diagenesis occurring in the region, such as burial and weathering. Many studies on continuous transformations from montmorillonite to mica have been made by investigators in various countries (Powers, 1959; Burst, 1959; Shutov et al., 1969). However, such a mode of occurrence has not been reported in Japan for interstratified minerals. Weaver and Bates (1952) and Weaver (1953) found interstratified minerals in sedimentary rocks of the Ordovician period, and demonstrated that the minerals were formed from tuffaceous sediments. Weaver (1959) also reported an interstratified mica/montmorillonite formed from K-bentonite (meta-bentonite). The kaolin beds associated with the coal beds of Carboniferous formations (the so-called tonstein) in Europe are considered to have been formed from volcanic ash, and interstratified mica/montmorillonite with the properties of K-bentonite has been found in them (Stoffler, 1963; Price and Duff, 1969; Spears, 1970). In America, Schultz (1 963) has also reported the occurrence of an interstratified mica/montmorillonite formed from volcanic ash of Pennsylvanian age. Such occurrences appear to be identical to that of the interstratified mineral found in the tuffaceous sediments of coalfields in Hokkaido. 8.1.2. Interstratifed minerals occurring in the so-called Green Tufs Although interstratified chlorite/montmorillonite occurs widely in the socalled Green Tuff, interstratified mica/montr,orillonite is observed oiily occasionally in certain specific districts. When Negishi ( I 967) studied the Miocene pyroclastic rocks near Minakami City, Gunma Prefecture, he noticed the occurrence of interstratified mica/montmorillonite in some samples collected from the rocks. In this district, acidic pyroclastic rocks, shale, sandstone and andesitic rocks occur, but the interstratified minerals were found only in the acidic pyroclastic rocks. They occur in association with chlorite and mica but not

268

INTERSTRATIFIED MINERALS

with montmorillonite and zeolites. The ratios of mica and montmoiillonite in the minerals differ considerably from specimen to specimen, and no continuous transformation from montmorillonite to mica through interstratified minerals has been observed. This suggests a very complex mode of formation for the interstratified minerals based on the detailed geological conditions in this district. Negishi (1967) has pointed out that differences in primary rocks may control the formation of the interstratified minerals. In the Green Tuff region, volcanism is commonly observed and the effects of such volcanism and hydrothermal solution must also be considered in relation to the formation of interstratified minerals, in addition to diagenesis. In the above district, interstratified mica/montmorillonites are found widely, but interstratified chlorite/montmorillonite is usually dominant in the so-called Green Tuff. Yoshimura (1961, 1964, 1971) has demonstrated the occurrence of interstratified chlorite/montmorillonites in the so-called Green Tuff formation of the Oshima-Fukushima district, Hokkaido. In this district, the Neogene Tertiary system is widely distributed and belongs to the so-called Green Tuff, The rocks in the district consist of pyroclastics that include rhyolite, dacite, andesite and basalt. The interstratified chlorite/montmorillonite occurs chiefly as a replacement product of volcanic glass fragments and as a cement in the matrix of andesitic and dacite tuffs, tuffaceous sandstones and tuff breccia. The relative percentage of expandable layers in the interstratified minerals decreases successively from the upper to lower part of the formation. The minerals found in the upper part usually contain small amounts of analcime as an impurity, while the minerals in the lower strata contain laumontite. Interstratified mica/ montmorillonite also occurs in this district but is found only in rhyolitic pyroclastics. Interstratified chlorite/montmorillonite has recently been found filling amygdales of basalt and replacing glass fragments in basaltic tuff breccia of the socalled Green Tuff (Hayashi et al., 1961; Yoshimura, 1971;Kimbara et ul., 1971; Kimbara and Shimoda, 1972;Kimbaraand Sudo, 1973;Kimbara, 1975a,b).Kimbara and Sudo (1973) investigated many specimens of chlorite and interstratified chlorite/montmorillonite from the Green Tuff of the Yamanaka district, Ishikawa Prefecture. The minerals studied vary from interstratified chlorite/montmorillonite to chlorite through so-called swelling chlorite. However, the mineralogical data for the interstratified minerals themselves were almost constant in their specimens, even though the formation including the interstratified minerals has a composite thickness of about 300 m. 8.1.3. Interstratified minernls occurring in the alteraticn area around so-called

Kuroko deposits

The origin of the so-called Kuroko deposits has been extensively studied in Japan. They usually occur at a particular horizon in Tertiary sediments, and it is considered that submarine volcanic activity may well have played an impor-

MODES OF OCCURRENCE

269

tant role in their formation. The Kuroko deposits may be grouped into two types according to their origin: (1) hydrothermal deposits around volcanic vents, which represent the source of eruption, and (2) deposits accumulated on the sea bottom around the volcanic vents. The origin of the clay minerals occurring in association with the Kuroko deposits is very complex and it is impossible to ascribe them simply to hydrothermal alteration or to diagenesis. Although their origin is thus unclear, clay minerals are always found around the deposits and consist mainly of mica, chlorite, montmorillonite and interstratified minerals. Although it appears to be unusual, a mineral assemblage characterized by diaspore, pyrophyllite and kaolinite has also been reported by Sudo and Hayashi (1957), Sudo et al. (1961) and Hayashi (1961). Sudo (1954) first described an interstratified mica/montmorillonite mineral from the alteration area around the Tsutsumizawa ore body of the Hanaoka mine, which is one of the typical Kuroko mines in Japan. The Tsutsumizawa ore body is of the stockwork type having a multiple pipe-like form with lateral extensions. The origin of the ore body is considered to be mainly hydrothermal. The ore minerals include galena, sphalerite, pyrite, gypsum, etc. and the actual mineral assemblage varies from place to place in the ore area. It may be rich in galena and sphalerite (black ore), rich in pyrite (yellow ore), rich in silica (siliceous ore), or rich in gypsum. The ore minerals are found as massive bodies without quartz, or as network veins in the siliceous part. Generally speaking, the ore bodies are enclosed by a chlorite-mica zone which grades into a montmorillonite zone outwards through an intermediate zone. However, some relations exist between the mineral assemblages and ore texture. Massivepyrite ore bodies: small amounts of kaolinite and diaspore are found in the peripheral portions associated with chlorite and mica; the chlorite is usually rich in Mg. Massive galena and sphalerite ore bodies: small amounts of kaolinite and diaspore are also found in the peripheral portions of the ore bodies associated with chlorite but without mica; beautiful prismatic diaspore crystals occur in the interspaces between the ore minerals ; an interstratified dioctahedral chlorite/ montmorillonite was taken from the intermediate zone. Siliceous ore bodies: the alteration products are composed mainly of mica; random interstratifications of mica and montmorillonite occur in the intermediate zone or as fillings of small fractures in the ore bodies. Gypsum ore bodies: the alteration products consist mainly of Mg-rich chlorite and mica; random to regular or almost regular interstratifications of mica and montmorillonite are found in the intermediate zone. Sudo and Hayashi (1955) found interstratified mica/montmorillonites with a reflection of about 27 A in alteration areas of the Kamikita and Aomori mines. The Honko ore body of the Kamikita mine is of the stockwork type having pyrite as its principal ore mineral. The inner zone of the alteration halo is composed largely of pyrophyllite and diaspore accompanied by kaolinite. The inner

270

INTERSTRATIFIED MINERALS

zone grades into a pyrophyllitized zone and then unaltered rhyolite progressively outwards. The kaolinite is generally well crystallized and often occurs together with diaspore crystals, filling the interspaces between pyrite crystals. Pyrite is also found over the entire area as impregnated crystals or veinlets. A regular or almost regular interstratified niica/montmorillonite is found in the interspaces between pyrite crystals (Sudo and Kodama, 1957; Hayashi, 1961). An interstratified dioctahedral chlorite/montmorillonite occurs in association with mica in a pyrite veinlet in weakly altered rhyolite. The clay minerals occurring in the alteration area around the ore bodies of the Shakanai mine, Akita Prefecture, consist mainly of mica minerals, chlorite and montmorillonite. Mica is recognized in close association with the black ore bodies, and randomly interstratified mica/montmorillonites also occur in the hanging wall of the ore bodies (Otagaki, 1968; Ishizaka, 1969; Otagaki et al., 1969; Shirozu and Higashi, 1972; Shirozu et al., 1972; Shimoda, 1972; Shimoda and Nishiyama, 1973). Interstratified minerals with a long spacing reflection are found in certain special parts of the alteration area such as the contact region of liparitic rocks and in the alteration zones along fissures and faults (Ishizaka, 1969). Shimoda et al. (1969a,b) have described two specimens from the alteration areas of the Iwami and Kurosawa Kuroko mines. In the former case, the mineral was found in and around the Kuroko ore body and consisted of a randomlyinterstratified mica with montmorillonite which resembled 1Md mica. At the Kurosawa mine, a zonal distribution of clay minerals can be recognized and mica with a IM polymorph is dominant in the inner part of the ore body. The outer zone is characterized by montmorillonite. Interstratified mica/montmorillonite is always found in the area between the mica and montmorillonite zones. The first report of the occurrence of interstratified chlorite/montmorillonite in the alteration areas of so-called Kuroko deposits was that given by Sudo (1954). He found a mineral with a spacing of about 30 A at the Tsutsumizawa ore body of the Hanaoka mine, Akita Prefecture. Although the specimen studied contains an appreciable amount of kaolinite as impurity, the magnesium detected by chemical analysis is very small and the chemical properties of the mineral resemble those of the Kurata specimen (interstratified dioctahedral chlorite/ montmorillonite) described by Sudo et al. (1954a,b). Subsequently, Sudo and Kodama (1957) undertook mineralogical studies of the interstratified dioctahedral chlorite/montmorillonite found by Sudo and Hayashi (1957) and Sudo et al. (1958) in the Kamikita mine. This mine includes several ore bodies such as those of Kaminosawa, Okunosawa, Tateishi and Honko. These ore bodies are accompanied by clayey altered zones composed mainly of kaolinite, mica and montmorillonite. Pyrophyllite and diaspore are occasionally detected byX-ray analysis (Sudo and Hayashi, 1957). The interstratified mineral was found in a pyrite veinlet in weakly altered rhyolite. This mineral is usually associated with mica.

MODES OF OCCURRENCE

27 1

Following the work of Sudo and Kodama (1957), many investigations were made on interstratified minerals (Sudo et al., 1958; Sudo, 1959a,b; Osada and Sudo, 1961; Sudo et al., 1961; Hayashi, 1961; Sugiura, 1962). In these reports, Osada and Sudo (1961) demonstrated the occurrence of almost regularly interstratified trioctahedral chlorite/montmorillonite and a mineral with the properties of socalled swelling chlorite. Sugiura (1962) discovered a regularly interstratified trioctahechal chlorite/montmorillonite in the alteration area of the Noto gypsum mine (a Kuroko-type mine) at Noto, Ishikawa Prefecture. This mineral occurs in association with gypsum and sulfide minerals in the altered shale around and within the ore body. It has been described as an interstratified chlorite/vermiculite. Recently, Shirozu et al. (1975) have reported mineralogical data for certain interstratified chlorite/montmorillonites collected from the intensively argillizedzones of various Kuroko and Kuroko-type gypsum deposits. Randomly interstratified trioctahedral chlorite/montmorillonite also occurs widely in the alteration area of Kuroko deposits (Osada and Sudo, 1961; Shirozu, 1969; Shimoda, 1970; Shirozu et al., 1975). Shimoda (1970) reported that a mineral from the Hanaoka mine exhibited the properties of the so-called swelling chlorite described by Honeyborne (1951), Stephen and MacEwan (1951), and Martin Vivaldi and MacEwan (1957, 1960). Subsequently, Shimoda (1974a) investigated two chlorite-like specimens having a spacing of about 14.8 A and showed that one can be described as a randomly interstratified trioctahedral chlorite/montmorillonite, although the other is not. Shirozu (1969) and Shirozu et a/. (1975) reported that the minerals with similar properties occurring in the alteration areas of Kuroko and Kuroko type gypsum deposits consist of randomly interstratified trioctahedral chlorite/montmorillonite. There are no reports so far of the occurrence of randomly interstratified dioctahedral chlorite/ montmorillonite. 8.1.4.

InterstratiFed minerals occurring in diaspore-pyropliyllite deposits

Interstratified mica/montmorillonite from diaspore-pyrophyllite deposits was first described by Takeshi (1958) in the Kanakura mine, Nagano Prefecture. Sudo (1959a,b) also demonstrated the occurrence of an interstratified micalmontmorillonite in the diaspore-pyrophyllite deposit at the Yonago mine, Nagano Prefecture. Later, Shimoda (1960), Shimoda and Sudo (1960), and Sudo et al. (1962) studied the mineral in detail, and gave geological and mineralogical data for it. Based on their studies, the interstratified mineral at the Yonago mine can be said to occur in close association with diaspore and pyrophyllite. The area near the deposit consists of fine-grained sandstone and shale which are intruded by porphyrite and andesite dykes. The diaspore-pyrophyllite ore occurs along the boundary zone between the porphyrite and andesite dykes, replacing both these materials. The confirmed minerals are diaspore, pyrophyllite, mica, kaolinite, rnontmorillonite, quartz and pyrite. The pyrophyllite and diaspore are found in two differentlocations but the zonal distribution is confirmed as (diaspore-pyro-

272

-

-

INTERSTRATIFIED MINERALS

phyllite) (kaolin minerals) (quartz), progressively away from the center. Interstratified mineral with a 26 A reflection is found in the cavities of the massive diaspore ore, and occurs frequently as vein-shaped masses in the pyrophyllite body. Mica is distributed in small amounts throughout these zones, while montmorillonite occurs rarely in the kaolinite zone. Shimoda (1960) demonstrated the occurrence of a mineral with identical properties in the pyrophyllite deposit of the Honami mine, Nagano Prefecture. A similar mineral from the Goto mine, Nagasaki Prefecture, occurs as a vein-like mass crossing the diaspore and pyrophyllite ore (Sudo et al., 1962). Recently, an interstratified mica/montmoriIlonite was found in the pyrophyllite-diaspore deposit of the Shokozan mine, Hiroshima Prefecture (Kakitani and Morita, unpublished data). Nishiyama et al. (1975) also reported a similar mineral from the pyrophyllite ore body of the Tohoo mine, Aichi Prefecture. The interstratified chlorite/montmorillonite found in diaspore-pyrophyllite deposits is dioctahedral. Interstratified dioctahedral chlorite/montmorillonite was first discovered from the Kurata kaolinite-type Roseki mine, Yamaguchi Prefecture. The mineral is found as lenticular vein-shaped masses in the clayey part. The degree of crystallinity of the kaolinite ranges from the well-crystallized state showing triclinicity to the disordered state. The interstratified mineral tends to occur in close association with comparativelydisordered kaolinite (Sudo et al., 1954a,b). The interstratified mineral from the Tohoo mine contains a small amount of lithium but no magnesium (Nishiyama et al., 1975). The mineral occurs in a clayey vein about 10 cm in width which cuts across the diasporepyrophyllite ore body. At this mine, interstratified mica/montmorillonite occurs widely together with pyrophyllite and mica. The interstratified dioctahedral chlorite/montmorillonite is usually associated with the interstratified mica/ montmorillonite but never with the pyrophyllite. 8.1.5.

InterstratiJied minerals occurring in the so-called Toseki deposits and in the alteration area of liparitic rocks

Toseki is composed mainly of mica, kaolinite and quartz, and is used as a raw material for chinaware. Extensive geological and mineralogical studies have shown that Toseki is a hydrothermal alteration product of various original rocks such as rhyolite, lithoidite and perlite. Kanaoka (1968) undertook mineralogical studies on Uebi and Izushi Toseki specimens and demonstrated that they consist mainly of interstratified dioctahedral chlorite/montmorillonite. Recently, Kanaoka (1974, 1975) has investigated many Toseki specimens from different localities and shown that they usually contain interstratified mica/montmorillonite and/or interstratified dioctahedral chlorite/montmorillonite. The Funyu Toseki deposit at the Funyu mine, Tochigi Prefecture, is an alteration product of liparite and is composed mainly of regularly interstratified mica/montmorillonite with small amounts of mica, pyrophyllite and kaolinite.

MODES OF OCCURRENCE

273

The mineralogical properties of the interstratified mineral occurring at the mine are similar to those of allevardite (Shimoda et al., 1974). The interstratified dioctahedral chlorite/montmorillonites found in some Toseki deposits are almost magnesium free, although the minerals from Kuroko deposits generally contain appreciable magnesium. The minerals from the Uebi and Izushi Toseki mines are dioctahedral without magnesium (Kanaoka, 1968). The Izushi Toseki deposit has been studied geologically by Tsukawaki (1962) and is considered to be an alteration product of pitchstone intruded into liparitic rocks. The clay and non-clay minerals detected in the deposit show a zonal distribution. The mineral zones from the outer part of the pitchstone to the inner part may be summarized as follows : (1) opaline silica (pitchstone), (2) montmorillonite with small amounts of cristobalite and mordenite, (3) interstratified mica/montmorillonite, (4) interstratified dioctahedral chlorite/montmorillonite, and ( 5 ) mica zones. The clay used as Toseki is a mixture of interstratified mica/montmorillonite and interstratified dioctahedral chlorite/montmorillonite. Mica occurs in the inner part of the deposit, and the clay which is rich in interstratified dioctahedral chlorite/montmorillonite forms an excellent raw material for chinaware. Ichikawa and Shimoda (1976) recently found an interstratified dioctahedral chlorite/montmorillonite closely associated with kaolinite and interstratified mica/montmorillonite in the Hokuno Toseki mine, Gifu Prefecture. The Toseki is an alteration product of liparite. The interstratified dioctahedral chlorite/ montmorillonite reported by Shimoda (1970) from the Takatama mine, Fukushima Prefecture, occurs in an alteration area of tuff and tuffaceous sediments formed by the intrusion of acidic rocks. The alteration products are not used as Toseki but the mineral assemblage, which consists of montmorillonite, kaolinite, interstratified mica/montmorillonite and interstratified dioctahedral chlorite/ montmorillonite, resembles that of a Toseki deposit. 8.1.6.

Interstratified ininerals occurring in geothermal areas

Interstratified minerals formed by hydrothermal alteration are widely distributed in active geothermal areas of Japan. The clay and clay minerals of geothermal alteration areas were first studied by Sumi (1968) in the Matsukawa geothermal district, lwate Prefecture. Shale, sandstone, conglomerate and welded tuff occur widely in this district and are covered by Quaternary volcanic rocks. Two or three hot springs are known and the rocks have been altered by hot spring action. The hydrothermally altered rocks may be divided into five zones based on the stability range of the minerals recrystallized. They are, from margin to center, as follows : the saponite zone, chlorite zone, montmorillonite zone, kaolinite zone, and alunite zone. The subterranean zonal arrangement of the altered rocks is very complicated but interstratified mica/montmorillonite is found only in the montmorillonite zone.

274

INTERSTRATIFIED MINERALS

Subsequently, in the geothermal area of the Hachimantai district, Akita Prefecture, interstratified mica/montmorillonite was found in the transition zone between the montrnorillonite and mica zones (Yora et al., 1973). Kimbara and Sumi (1975) also reported that interstratified mica/montmorillonite occurs in the transition area between the montmorillonite and mica zones in the Takinoue geothermal area, Iwate Prefecture. Hayashi (1972), and Hayashi and Yamazaki (1975) have reported interstratified mica/montmorillonites formed from pyroxene andesite under hydrothermal conditions in the Otake geothermal area, Oita Prefecture. The interstratified minerals occur only in the depth range from 320 to 860 ni, which corresponds to a measured temperature of from 120 to 270°C, and the montmorillonite component generally decreases with increasing depth. Although interstratified mica/montmorillonite occurs widely in geothermal areas, there are as yet no reports of the occurrence of interstratified chlorite/ montmorillonite in such areas. 8.1.7.

InterstratiJied minerals formed under weathering conditions

So-called acid clay is widely distributed in Japan. It is composed mainly of montmorillonite formed by alteration of volcanic ash and tuff, and usually contains small amounts of kaolin minerals, qualtz and cristobalite. The monlmorillonite in some acid clays has been partially altered by weathering, and interstratified kaolin/montmorillonite is frequently found in the clays. Sudo (1956), and Sudo and Hayashi (1956a,b) first discovered an interstratified mineral in the Awazu acid clay and showed that it had been formed from montmorillonite by weathering. Later, Shimoyama et al. (1969) collected a series of specimens ranging from almost pure montmorillonite to the interstratified mineral, with a progressive change in mineralogical properties from the montmorillonite towards the interstratified mineral. Akai (1974) collected a series of specimens from the weathered to non-weathered tuff bed at Chita, Aichi Prefecture. The non-weathered part of the tuff is composed of almost pure montmorillonite, but in the weathered part the montmorillonite shows no basal reflections and its properties resemble those of interstratified kaolin/montmorillonite. Interstratified kaolin/montmorillonite is ordinarily found in acid clay, but Kohyama (1972) has shown that the ironrich montmorillonite in the tuff at Oya, Tochigi Prefecture, is transformed by weathering to a mineral which resembles interstratified kaolin/montmorillonite. Biotite is easily converted to interstratified biotite/vermiculite (hydrobiotite) under weathering conditions (Kanno et al., 1960; Kato, 1965), and chlorite forms interstratified chlorite/vermiculite (Nishiyama and Oinuma, 1973; Nishiyama et al., 1973, 1974).

MINERALOGICAL PROPERTIES

215

8.2. THE MINERALOGICAL PROPERTIES OF INTERSTRATIFIED MINERALS

Numerous examples of interstratified minerals have been described in Japan. The following sections provide mineralogical data for some of the typical interstratified minerals. They may be divided into four groups as follows: interstratified mica/montmorillonite, interstratified chlorite/montmorillonite, interstratified kaolin/montmorillonite, and other interstratified minerals.

8.2.1. Interstratified micalmontmorillonite Interstratified mica/montmorillonite was first described by Sudo (1954), and Sudo and Hayashi (1955). However, critical studies were impossible due to the presence of impurities. In 1956, Sudo and Hayashi demonstrated that the minerals with a spacing of about 26 A found in the alteration areas of the Hanaoka and Kamikita Kuroko mines were interstratified mica/montmorillonites. Subsequently, many interstratified mica/montmorillonites were found in numerous localities, and detailed studies have been made. A. X-ray diffraction data

Generally speaking, these minerals can be grouped into random and regular types. The former type shows a broad reflection in the region of 10-15 A, and the latter shows a sharp reflection at about 24-27 A. Some of the regularly interstratified mica/montmorillonites described in Japan may in fact not be perfectly regular, since no mineral having identical properties to allevardite or rectorite has yet been found. X-ray diffraction data are given in Table 8.1. An interstratified mineral reported from the Goto mine, Nagasaki Prefecture, by Sudo et al. (1962) appears to be almost of the regular type. The specimen gives a sharp reflection at 25.3 A and its higher orders. Twelve basal reflections are recorded and they make a rational series based on the 25.3 A spacing. This indicates that the mineral is almost of regular type. The 25.3 A reflection expands to 26.5 A on treatment with ethylene glycol and twelve higher order reflections are also clearly recorded. Although the reflection shifts to 19.6 A on heating at 55Q°C,it shows a slight tail to the low angle side. A mineral with identical properties has been described by Manaoka (1974) and Shimoda et al. (1974) from the Funyu Toseki mine, Tochigi Prefecture. A specimen found by Shimoda and Sudo (1960) at the Yonago mine gives a sharp reflection at 27.6 A and its higher orders. Although ten basal reflections are observed, a slight disagreement in the (001) and 2 X d(002) spacings indicates that the mineral is not of completely regular type. When treated with ethylene glycol, the 27.6 A reflection moves to 28.5 A. On heating at 550 and 700" C, the 27.6 A reflection shifts to 10 A, and it tailed to the low angle side of the reflection peak. The 19 A reflection cannot be detected by such treatments, but at 900°C a weak and broad reflection appears at about 19 A. The mineral was judged by Shiinoda et al. (1969a) to be an interstratified mineral with 60% mica

276

INTERSTRATIFIED MINERALS

TABLE 8.1. X-Ray diffraction data of interstratified mica/montmorillonites 1)

2)

3)

001 002 003 004

25.3(2024) 12.7(745) 8.58(5) 6.274(4)

27.6(3 349) 12.98(1856) 9.21(36)

005 006 007 008 009

5.007(81)

5.059(168)

3.545(12) 3.1 29(94) 3.761(4)

3.558(61) 3.252(237) 2.820(12)

00,lO w,11 00,12 00,13

2.513(4) 2.236(3) 2.070(8) 1.920(11)

2.562(41)

2.56(6)

2.065(44) 1.971(33)

1.99(2)

23.9 Ilt 0.5+ 22.2 & 0.3+ 24.5 f 0.3+

Nat. Na-f Ca-f

EG GL Na

+ GL Ca + GL

27.6 f 0.5+ 27.1 f 0.3+ 27.0 & 0.3+

H2O 100°C 200 300 400 450 500 600 700 750 800 900

25.3+

26.5 28.5

23.6 5 0.5+ 22.7 & 0.5+ 25.0 f 0.5+

26.1 5 1.0

5.07(12) 4.48( 10) 3.52(7) 3.19(11)

23.9 f 1.0+ 22.1 & 0.8+ 24.4 & 0.8+

28.5 27.8 & 0.3+ 27.2 & 0.3+ 27.1 & 0.3+

27.9 5 0.5' 27.4 f 0.5+ 26.9 f 0.5+

28.8

29.2

24.5

10.3

19.6

26.8(36) 12.6(36) 9.21(3)

(19) 20.5

9.9

27.9

28.7

-

12.3

9.94

- 11.5 9.98

19.6

19.6

(19)

19.6

19.6

(19)

-

10.0 11.8 (24.5, weak) 10.3 (18.4, weak)

10

10

10

10

+ HCI + + EG + HzO + HzO HzO + EG KOH + KCl

700°C 700°C HCI 800°C 900°C

KOH LiN03 LiNO3

22.7

+ EG

22

MINERALOGICAL PROPERTIES

5)

8) 9) Ki Kz d(A) d(A) d(A) d(A) d(A)(Z) d ( A ) 4% 29.4(1990) 27.6(2467) 27.6(2468) 25.9(332) 29.4(2000) 29.4 27.2 12.9(644) 12.98(1252) 12.80(1985) 12.50(152) 11.8(1418) 11.9 12.45(518) 8.4(24) 9.35(40) 8.61(12) 9.2(25) 6.320(4) 6.754(11)

4)

5.063(74) 5.152(220)

6)

277

7)

5.090(284) 5.006(159) 5.068(203) 5.07

4.073(6) 3.587(26) 3.630(32) 3.587(78) 3.218(83) 3.230(285) 3.206(252) 2.820(3) 2.811(33) 2.753(14) 2.562(9)

2.576(14)

2.092(9) 2.102(35) 1.951(20) 1.988(60)

2.554(8) 2.065(44) 1.955(42)

3.545(29) 3.503(34) 3.129(176) 3.232(206) 3.28 2.769(4) 2.819(4) 2.506(5) 2.263(3) 2.070(11) 1.920(21)

10)

11)

d(A) 38.4(100) 18.3(34) 11.6(93) 9.00(16)

d(A) 11.0(100) 5.006(60) 4.502(27) 4.370(7) 4.130(2)

3'6601

5.07(65)

3.573 (8)

3.325(45) 3.076(20) 3.180(76) 4.91(20) 2.938(8) 2.903(14) 2.590 2.5693 (25) 3.20(74) 2.466 1.965(11) 1.94(16) 2.477 (3) 2.390(7)

2.562(10)

]

2.056(28) 1.980(28)

26.04+

27.5

25.2

29.4

29.4

31,27.72+ 29.4 30,28.02+

30

26.6 27.6

31.5 32.0

11.9 29.4 12.8

30.5

10

36.1 35.3 10.2 9.90

29.4 19.6 19.6

9.98 9.98

9.94

26.0

9.94 10.1 10.1

10.3 25.0

10.3

19.6

10.2

9.92

10.2

10.5 25(weak) 11.6

12.3

10.3

11.0 22.6

27.2

27.1

32.0 27.6 10.3 29.4

22.5

11.2

25.2 27.2

16.4 18.2

25.2

(Continued)

278

INTERSTRATIFIED MINERALS

TABLE 8.1-Continued

_.

NH4N03 -

Probability coefficients P(A) P(B) P(AA) p(AW

P@B) P(BA)

0.50 0.50 0.20 0.80 0.30 0.70

0.55 0.45 0.75 0.25 0.10 0.90

0.60 0.40 0.88 0.12 0.00 1 .oo

Basal spacing: Values for the X-ray diffraction peak occurring at the smallest glancing angle on each chart. Nat: Natural state. Na-f, etc.: saturated with sodium ions, etc. EG: Ethylene glycol. GL: Glycerol. Na-GL, etc.: saturated with sodium ions and successively treated with glycerol, etc. HzO: saturated with water. 700°C HCI, etc.: heated at 700°C and successively treated with hydrochloric acid, etc. KOH KCI, etc.: Treated with KOH solution and successively treated with KCI, solution, etc. Probability coefficients: P(A), mica layers ;P(B) expandablelayers. Mean values or corrected values. 1) the Goto specimen from the Goto mine, Nagasaki Prefecture (Sudo et al., 1962; Kodama et al., 1969; Shimoda et al., 1974). 2) the Yonago specimen from the Yonago mine, Nagano Prefecture (Shimoda and Sudo, 1960; Kodam et al., 1969; Sudo et al., 1962; Shimoda et al., 1969a,b). 3) the Honami specimen from the Honami mine, Nagano Prefecture (Sudo ef al., 1962; Kodama et al., 1969).

+

+

+

and 40 % expandable layers. Subsequently, other interstratified minerals with similar properties were reported by various investigators (Shimoda et al., 1969 b; Tomita et al., 1969; Tomita and Dozono, 1974; Hayashi and Yamazaki, 1975; Sat0 et al., 1975; Tomita et al., 1975). A specimen obtained from the Honami mine also exhibits a sharp reflection at 26.8 A. The reflection shifts to 10 A on heat treatment but no reflection appears at about 19 A after heating. In general, minerals such as the Goto, Funyu, Yonago and Honami specimens show a high ability for rehydration (Shimoda et al., 1969b; Tomita and Dozono, 1973). A specimen from the Takatama mine clearly rehydrates in air after heating at 800°C (Shimoda et al., 1969b). An interstratified mica/montmorillonite found in the alteration area of the Niida Kuroko-type mineralized zone near the Shakanai mine, Akita Prefecture, has been studied critically by Shimoda (1972). The material exhibits a reflection at about 29.4 A and its higher orders. A comparison of the X-ray diffraction pattern with a theoretically calculated pattern based on Kakinoki and Komura’s equation (1952, 1954) indicates that the interstratification may approximate to a random stacking of 55-65 % mica and 45-35 % expandable layers, although there was a slight difference between the observed and calculated spacings. The Fourier transform method indicates the existence of 10, 12.5 and 15.5 A layer components in the interstratification. However, after saturating with glycol for

279

MINERALOGICAL PROPERTIES

0.6 0.4

0.65 0.35

0.6 0.4

0.75 0.25

0.72 0.28 0.61

-

0.00

-

0.55 0.45 0.18 0.82 0.00 1.oo

0.7 0.3 0.4 0.3 0.0 0.3

0.87 0.13

4) the Niida specimen from a mineralized area of the Kuroko region at Niida, southern part of Odate, Akita Prefecture (Shimoda, 1972). 5) the Takatama specimen from the Takatama mine, Fukushima Prefecture (Shimoda et al., 1969b). 6) the Kurosawa specimen from the Kurosawa mine, Fukushima Prefecture (Shimoda et al., 1969b). 7) the Funyu specimen from the Funyu mine, Tochigi Prefecture (Shimoda ei al., 1974). 8) the Kamisunagawa specimens from the Kamisunagawa coal-field district, Hokkaido. K1 is the specimen described by Shimoda et al. (1969b) and K2 is the specimen described by Kobayashi and Oinuma (1960) and analyzed by Sat0 et al. (1965). 9) the specimen found in a hydrothermally altered andesite in the southern part of the Satsuma Peninsula, Kagoshima Prefecture (Tomita and Dozono, 1973). 10) the Tokura specimen found in a hydrothermally altered tuff at Tokura, Gunma Prefecture (Kizaki, 1970: Sato and Kizaki, 1972). 11) the Iwami specimen from the Iwami mine, Shimane Prefecture (Shimoda et al., 1969a).

1 week the Fourier transform indicates the presence of only 10 and 18 8, layer components and the curve is identical to that given by Cole (1966). The curve indicates that the interstratification is composed of a two-component stacking of about 60 % mica and 40 % montmorillonite layers, where montmorillonite layers never succeed consecutively. The same type of mineral, of the same or similar origin, has been found in many localities (Hayashi, 1961; Shirozu et al., 1972; Shirozu, 1974; Shirozu and Higashi, 1974; Higashi, 1974; Higashi and Shirozu, 1975). In general, the interstratified minerals found in the so-called Green Tuff are associated with chlorite, mica, montmorillonite and certain other interstratified minerals. Therefore, it is usually impossible to undertake detailed studies on the impurities, although they are considered to be randomly interstratified minerals having 001 reflections in the regions of 24-29 A and 10-15 A. A specimen found at Tokura, Gunma Prefecture, by Kizaki (1970) has been studied mineraalogically and geologically, although it contains small amounts of chlorite, mica, quartz and calcite as impurities. The specimen was derived from hydrothermally altered tuffaceous sediments of the so-called Green Tuff. It gives a reflection at 38 8, and its higher orders, but there is no rational series based on the 38 8, spacing. The 38 8, reflection shifts to 40.2 8, on treatment with ethylene glycol. When heated at 4OO0C, it disappears and a 9.90 8, reflection newly appears. The

280

INTERSTRATIFIED MINERALS

interstratification of the mineral has been confirmed by Sat0 and Kizaki (1972) by comparing the observed and calculated X-ray patterns as follows: P(A) = 0.7 (the probability of the existence of mica layers), P(B) = 0.3 (the probability of the existence of montmorillonite layers), P(AA) = 0.4, P(AB) = 0.3, P(BA) = 0.3, P(BB) = 0.0, and g = 2 (the range of correlation). A mineral with such properties was first described by Hayashi (1961) from the Kamikita mine. It was not studied critically, although it shows a reflection at 36.8 A and the behavior on treatment with ethylene glycol or heat closely resembles that of the mineral described by Kizaki (1970). An interstratified mineral found in a tuff bed of the coalfield district of Kamisunagawa was first described by Kobayashi and Oinuma (1960). Sat0 et al. (1965) later studied the interstratification mineralogically. The specimen shows a weak reflection at 29.4 A and its higher orders, but the reflections exhibit no rational series in the highest spacing. The 29.4 A reflection disappears on heating at 450°C and a 9.94 A reflection with higher orders appears. On treatment with ethylene glycol, the 29.4 A reflection disappears and the 11.9 A reflection splits into two peaks at 11.9 and 9.51 A. Sat0 et al. (1965), using Kakinoki and Komura’s equation (1952, 1954), estimated that the mineral to be an interstratified mineral with 72 % mica and 28 % montmorillonite components, where the probability of finding mica succeeding mica components was 0.61 1. Later, Shimoda et al. (1969a,b) also found interstratified mica/montmorillonites in a different tuff bed from the same coalfield district. So-called randomly interstratified mica/montmorillonite has been reported from many localities and with different modes of occurrence. However, critical descriptions of its mineralogy have not been given since the mineral usually contains certain kinds of impurities. Shimoda et al. (1969b) obtained a mica with an 11 A reflection from the Iwami Kuroko mine, Shimane Prefecture. Its X-ray pattern is similar to that of 1 M mica but the 11 A peak splits into two peaks at 11.5 and 9.93 A on treatment with ethylene glycol. When heated at 5OO0C, it gives a 10.2 A reflection and its higher orders. Shimoda et al. have reported that the material is an interstratified mineral having about 87 % mica and 13% montmorillonite layers. Randomly interstratified minerals which are similar to mica have been reported by many investigators and from many localities (Shirozu, 1974; Shirozu et al., 1972; Higashi, 1974; Higashi and Shirozu, 1975; Nishiyama et al., 1973; Shimoda and Nishiyama, 1973). B. Differential thermal analysis (DTA)

Variations in DTA curves have been ascribed to differences in polymorphic forms, chemical composition and interstratifications, as well as to the method of sample preparation and instrumental conditions. Although recently so-called micro-DTA, which is a DTA method using a very small amount of specimen, has been developed in Japan, the DTA curves discussed here were recorded with the usual DTA apparatus using about 50-200 mg of specimen. The most obvious DTA effects in interstratified minerals are related to evaporation of bound water

MINERALOGICAL PROPERTIES

28 1

and hydroxyl water molecules. The first endothermic peak appears at about 100-200°C, which is usually a double peak, and the temperatures vary with the cations and the water molecules in the interlayer (Hendricks et al., 1940). The second peak, in the 500-800°C range, accompanies the loss of hydroxyl water molecules and provides useful information about the interstratified minerals. As shown in Fig. 8.1, the specimens from the Goto and Yonago mines yield a single endothermic peak in the 500-600°C range. On the other hand, the specimens from the alteration areas of the Iwami Kuroko mine and Niida mineralized district and the two specimens from the tuffaceous sediments at Kamisunagawa, exhibit two endothermic peaks in the 500-700°C range. It has frequently been stated that the double hydroxyl endothermal peak is caused by the two individual layers forming the interstratified minerals, where the mica layers cause the Iower peak and the niontmorillonite layers the higher peak. Shimoda et al. (1969a) have shown that the two types of dehydroxyl curves observed by DTA, i.e. those with single and double peaks, are related to origin. The former

1000

0 Temp. ( - C )

Fig. 8.1. DTA curves of interstratified mica/montmorillonites. G : the Goto specimen (Sudo el a!., 1962). Y : the Yonago specimen (Shimoda and Sudo, 1960). I: the Iwami specimen (Shimoda et al., 1969a). S : the Niida specimen (Shimoda, 1972). K1: the Kamisunagawa specimen (Shimoda et al., 1969b). K2: the Kamisunagawa specimen (Kobayashi and Oinurna, 1960).

INTERSTRATIFIED MINERALS

282

TABLE 8.2. Chemical analysis of interstratified mica/montmorillonites

* Chemical composition SiOz A1203 A1203 Fez03 FeO MnO MgO CaO(f) CaO(1)

(%)

NazO KzO HzO(+) HzO(-) Total Structural formula Si AI(1V) AI(V1) Fe3+ Fez+ Mg Ti Ca Na

K Exchangeable Ca Mg

+

54.54 0.01 39.45 0.07

1)

44.80 33.88

* 55.08 1.40 35.67 0.28

0.39 0.00 0.44

2)

* 43.17 0.51 33.54 0.26 0.13

1.24

0.00 0.41

0.65

1.72

10.97

0.03 1.32

10.52

1.96 1.99 (5.36) (5.99)

1.88 1.13 6.91 8.13

0.35 5.92 (5.90) (4.55)

0.38 0.28 10.48 7.75

99.33

12.94 3.06 7.97 0.01

6.18 1.82 3.67

0.16

0.01 0.32

0.20 0.90 0.60

0.14 0.50 0.20

0.44

54.9 1.5 36.3 0.3

0.16 0.19 0.01 0.17 1.84

6.21 1.79 3.83 0.02 0.01 0.14 0.08 0.10 0.51

0.34

044 Ozo(OH)4 044 Base CEC 61 47 Exchangeable cations on samples in the natural state MgO 0.23 CaO 0.97 NazO 0.16 KzO 0.02

45.44 1.54 33.37 0.26

0.0 0.3

9.9 0.05 0.9 4.9 (5.8) (3.7)

100.23

13.37 2.63 7.58 0.03

3)

1.10 10.06 0.65 1.96 7.48 7.40 S:0.14 99.40

13.3 2.7 7.6 0.1 0.1 0.2 0.4 1.5

6.30 1.70 3.75 0.03 0.22

0.01 0.23 0.42

0.24 Ozo(OH)4 33

0.38 0.61 0.27 0.03

044

Ozo(OH)4

0.03 0.75 0.19 0.10

seems to derive from niica and the latter to be related to the presence of mica and montmorillonite layers. C. Chemical analysis

Chemical analyses for the interstratified minerals have been given by several

MINERALOGICAL PROPERTIES

47.13 0.33 31.76

44.95 31.77

47.51 0.23 29.91

44.76 0.14 33.26 0.74

283

49.15 0.00 28.79 0.92

52.64 0.38 27.77

45.82 0.49 29.83

0.98 0.89

14.98 0.02 3.94

tr 0.35

0.02

0.99

0.00

1.52

2.02 2.22

10.94

10.91

11.63

2.14

11.22

1.28

0.04 2.85 8.66 6.97

tr 4.55 9.79 6.36

0.30 5.14 4.41 9.26

2.07 2.59 6.76 8.11

0.77 2.88 7.43 6.60

0.24 3.72 6.50 3.04

0.80 1.40 8.32 5.04

99.90

100.00

100.08

100.57

99.28

99.58

100.64

6.34 1.66 3.89 0.08

6.92 1.08 3.69 0.10 0.31

6.76 1.24 3.58 0.09 0.10 0.43 0.04 0.17 0.61 0.06

6.66 1.34 3.99 0.01 0.07 0.04 0.14 0.01 0.51

0.02 0.57 0.46

0.18 0.21 0.52

tr

50.27 0.29 29.89 0.42

3.42

} 0.26 0.19 5.92 6.04 2.85 99.55

The chemical compositions in colums marked * were obtained by analysis of ignited samples. CEC: Values obtained on the basis of lOOg oven-dried sample. Note: Numbers 1-1 1 appeared correspond to those in Table 8.1.

authors. Most of the data listed in Table 8.2 were obtained by the standard wet method and the structural formulae were calculated on the basis of of a negative charge of 44 (= Oeo(OH)4). The chemical composition of the Goto specimen resembles that of mica, although there are of course fewer interlayer cations than in the case of mica.

284

INTERSTRATIFIED MINERALS

The content of NazO is slightly higher than in the Yonago specimen. The specimen from the Funyu mine is also characterized by a relatively high content of sodium in the interlayer position, and the two specimens from the Goto and Funyu mines resemble allevardite chemically. Interstratified mineral containing appreciable amounts of potassium, such as the Yonago specimen, is common in nature. As seen from the structural formulae, the ratio of AljSi in the tetrahedral positions of these minerals is close to that of mica. The composition of the Niida specimen roughly resembles that of mica. However, the ratio of AI/Si in the tetrahedral positions is lower than that of mica, and rather resembles that of montmorillonite. The two Kamisunagawa specimens give a low Al/Si ratio, the values being almost identical to that of montmorillonite. The interstratifications in the Kamisunagawa specimens reresemble that of the Yonago specimen. However, the AI/Si ratios in the tetrahedral positions are clearly different. According to Shimoda et al. (1974), the chemical compositions of the non-expandable and expandable layers in the interstratified minerals indicate a fairly wide range of AI/Si ratios in the tetrahedral positions. Based on the total chemical compositions, as expressed in the structural formulae, the interstratified minerals may be divided into two groups : (1) interstratified mineral consisting of a mica-like layer which is chemically similar to montmorillonite and an expandable layer with the properties of montmorillonite, and (2) interstratified mineral formed from non-expandable and expandable mica-like layers with the chemical composition of mica. The Kamisunagawa specimens apparently belong to the former group and the chemical properties of the silicate layer are the same as those of montmorillonite. On the other hand, the Goto, Funyu and Yonago specimens belong to the latter group and are closely similar to mica. D. Infrared absorption analysis

Although infrared absorption data have been reported for interstratified minerals by many investigators, critical studies have not yet been made. Assignment of the absorption bands represents an important problem for the future. Oinuma and Hayashi (1965) have compared the absorption bands of several interstratified minerals with those of the constituent minerals, and they late gave many infrared spectra for various clay minerals including interstratified minerals (Oinuma and Hayashi, 1968). As shown in Table 8.3, the OH-stretchingvibration bands of the minerals lie in the frequency region, 3600-3700 cm-l. In the Goto and Yonago specimens, the band is at 3650 cm-I and the spectra in the region are identical to those of allevardite and rectorite. On the other hand, the bands in the Niida and Kamisunagawa specimens appear at about 3630 cm-I and the spectra resemble that of rnontmorillonite (Shimoda and Brydon, 1971). The bands at about 1000 cm-l, which correspond to the Si-0 vibrations, are almost constant in the specimens considered here, although the spectra of alle-

285

MINERALOGICAL PROPERTIES TABLE 8.3. Infrared absorption band frequencies of interstratified mica/montmorillonites Allevardite 3650 S

Rectorite 3650 S

3440 M 1640 S 1120 Sh 1080 Sh 1053 S 1026 S 990 Sh 918 Sh 875 Inf

3430 M 1645 S

820 M 810 M

815 M

1083 Sh 1050 S 1028 S 990 Sh 916 Sh

735 M 710 Sh

750 Inf 735 s 710 Sh

645 Sh

640 Sh

549 s 483 S

547 s 483 S

Goto

3655 36401s 3420 M 1640 W

1020 s

Yonago 3650 S

Niida

Kamisunagawa-Kl

3420 M 1642 W

3630 S 3440 S,B 1640 W

3640 S 3445 M 1645 W

1022 s

1030 S,B 918 W

1035 S 995 Inf 924 M

830 Sh

830 M

760 W

760 M

685 Inf

695 W

620 Inf 535 s 482 S

625 Sh 530 S 478 S 420 W

930 Sh

930 M

820 M 810 Sh 750 Sh 725 M

820 M 810 Inf 758 M 728 W

540 S 477 s

540 S 477 s

Allevardite, rectorite and Yonago: Shimoda and Brydon (1971). Niida: Shimoda (1972). Kamisunagawa-K1 : Shimoda et al. (1974). S, Strong; M, Medium; W, Weak; Sh, Shoulder; Inf, Inflection; B, Broad;

vardite and rectorite are clearly different from those of the material found in Japan. In the case of the band at 820-830 cm-l, the Kamisunagawa and Shakanai specimens exhibit a single absorption at 830 cm-1 but the others show a distinct doublet band at 820 cm-l. The band at about 760 cm-l is also single in the case of the Kamisunagawa and Shakanai specimens but doublet in the others. Shimoda and Brydon (1971) have demonstrated that heat treatment of the minerals can provide important information on the component layers. For example, the Si-0 vibration band at about 1035 cm-l in the Kamisunagawa specimen persisted up to 800"C, although it shifted slightly to 1025 cm-l. The band at 1022 cm-I in the Yonago specimen persisted up to 700°C but split into two bands at 1043 and 998 cm-l on raising the temperature to 800°C. The behavior of the Yonago specimen on heating resembles that of the 2Mpolymorph of mica, while that of the Kamisunagawa specimen is closer to 1M mica. The montmorillonite specimen described by Shimoda and Brydon (1971) showed no splitting of the band on heating at 800°C. More important phenomena are observed in the bands and band shifts in the 800-500 cm-I region on heating. The 760 cm-l band of the Kamisunagawa

286

INTERSTRATIFIED MINERALS

specimen weakened and broadened at 500°C and a new absorption band appeared at 730 cm-l. The 535 cm-l band broadened at 45OOC and small absorption bands appeared at 528 and 566 cm-l at 550°C. On heating to 7OO0C, a new band appeared at 585 cm-l, although the 528 cm-l band disappeared. Bands at 585 and 566 cm-l are clearly seen in the spectra of specimens heated at 800°C. The above bands and band shifts resemble those of 1 M mica and montmorillonite. The strong band at 758 cm-l in the Yonago specimen remained in the same position on heating at 550"C, although it decreased in intensity. The weak 728 cm-l band shifted to 722 cm-l and increased in intensity. The band a t 540 cm-l shifted to 568 cm-1 and persisted up to 800°C. These bands and band shifts are comparable to those of 2M mica. Based on the above absorption characteristics, the interstratified minerals can be divided into two groups: (1) interstratified minerals that are composed of mica and montmorillonite, the characters of which are the same as those of the individual minerals, and (2) interstratified minerals that are composed of mica and its expandable layers, which have been referred to as hydrous mica complex by Shimoda and Sudo (1960). The absorption data of allevardite a.,d rectorite appear to fit the second group, although this identification remains tentative. E. Electron microscopy

Electron micrographs of the Yonago and Kamisunagawa-K1specimens show very thin and irregularly shaped particles, as illustrated in Figs. 8.2 and 8.3. These particles are clearly different from those of allevardite with a well-defined ribbon-like shape found at Allevard, France (Fig. 8.4). Shimoda and Nishiyama (1973), Nishiyama and Shimoda (1974), and Nishiyama (1975) have studied certain interstratified minerals using the oblique electron-diffraction technique. They distinguished the interstratified minerals into three types, which are apparently closely related to mica polymorphs. Yoshida (1976) directly observed the lattice image in the Kamisunagawa specimen, as shown in Fig. 8.5. 8.2.2.

Interstratijied chloritelmontmorillonite

Interstratified chlorite/montmorillonite was first discovered in the Roseki deposit at the Kurata mine, Yamaguchi Prefecture (Sudo, 1954; Sudo et aI., 1954a,b). Sudo et al. studied a mineral with a long spacing reflection and showed that it was composed of aluminum chlorite and montmorillonite. Minerals of this type have subsequently been discovered in the alteration areas of wall rocks of certain Kuroko deposits (Sudo, 1954; Sudo and Hayashi, 1955, 1956b, 1957; Sudo and Kodama, 1957; Sudo et al., 1958; Hayashi, 1961; Kimbara and Nagata, 1974), in some Toseki deposits (Kanaoka, 1968, 1974, 1975; Ichikawa and Shimoda, 1976), in some Roseki deposits (Mitsuda, 1957; Nishiyama et al., 1975), and in the alteration area of the Takatama mine, which has been worked as a vein-type gold-silver mine in Japan (Shimoda, 1969).

MINERALOC ICAL PROPERTIES

Fig. 8.2. The Yonago specimen.

Fig. 8.3. The Kamisunagawa-K1 specimen.

28 7

288

INTERSTRATIFIED MINERALS

Fig. 8.4. Allevardite from Allevard, France,

Fig. 8.5. Lattice image of the Kamisunagawa specimen (Yoshida, 1976).

MINERALOGICAL PROPERTIES

289

Studies on interstratified trioctahedral chloritelsaponite were initiated by Takahashi (1959). The material was obtained from a clayey vein in the dolomite ore of the Tsunemi mine, Fukuoka Prefecture. Subsequently, Sugiura (1962) found an interstratified trioctahedral chlorite/saponite (vermiculite) in the alteration area of the Noto mine, one of the Kuroko-type gypsum mines in Japan. Many other samples have been reported from the alteration areas of the so-called Kuroko deposits and in the so-called Green Tuff (Osada and Sudo, 1961; Shirozu, 1969, 1974; Shirozu et al., 1975; Yoshimura, 1971;Yoshimura and Kimbara, 1974; Katsumoto and Shirozu, 1973; Kimbara, 1975a,b; Kimbara and Sudo, 1973; Kimbara and Honda, 1975). Shimosaka and Sudo (1961) have reported an interstratified mineral characterized by a high iron content and low magnesium content from the Tertiary iron-sand bed at Gokan, Gunma Prefecture. A. X-Ray Diffraction data

The minerals with regular or almost regular interstratifications exhibit a sharp and strong reflection at about 30 A and its higher orders, as shown in Tables 8.4 and 8.5. These 30 A reflections disappear on heating at 300°C but reappear at about 24 A at 500°C. The 30 A reflection in the Takatama specimen shifts to 27.8 A at 300°C and the Fourier synthesis curve suggests the existence of a single layer of water molecules between the silicate layers (Shimoda, 1969). The other specimens give no reflection at about 27 A after heating at 300°C. The Gokan specimen from the Tertiary iron-sand bed exhibits no reflection at about 24 A after heating. It may decompose at 500°C. This behavior is apparently related to its chemical composition, since a high iron content usually leads to a decrease in the decomposition temperature of the minerals. The 30 8, reflections move to about 31 A on treatment with ethylene glycol and to about 27 8, after treatment with ammonium nitrate solution. The lattice spacings, d(OOl), of the interstratified chlorite/montmorillonites before and after certain treatments are listed in Tables 8.4 and 8.5. Randomly interstratified chlorite/montmorillonite has also been reported by various investigators (Osada and Sudo, 1961; Shirozu, 1969; Shirozu et al., 1975; Katsumoto and Shirozu, 1973; Shimoda, 1970, 1974a; Kimbara and Shimoda, 1972). The randomly interstratified minerals are composed of trioctahedral chlorite and saponite, and there is no report on the occurrence of randomly interstratified dioctahedral chlorite/niontmorillonite. As shown in Table 8.5, a specimen from amygdales in the pillow lava of the Sunakobuchi Formation at Nibetsu, Akita Prefecture, exhibits a sharp reflection at 14.82 8, and its higher orders (Kimbara and Shimoda, 1972). These reflections form an almost regular series based on the 14.82 A spacing, except for a weak reflection at 9.927 A. The 14.82 A reflection expands to 16.35 8, on treatment with ethylene glycol and shifts to 11.78 A on heating at 450°C. These changes in pattern before and after treatment indicate that the specimen is a randomly

TABLE 8.4. X-Ray diffraction data of interstratified dioctahedral chlorite/montmorillonites

-

001 001 002 003 004 005 006 007 008 009 00,lO

001t 060,331 300"C, 1 hr 300°C, 5 hr 450"C, 1 hr 500"C, 1 hr 600°C, 1 hr 700°C, 1 hr EG NH4H03 A B

1) 2) 3) d(A.)(Ot d(h(l)t d(W) 29.8 f 0.5(10) 29.6 f 0.2(10) 30.8(82) 14.7 f 0.1(18) 15.0(100) 14.7 f 0.2(15) 9.96(14) 10.3 (4) 9.8 f 0.1(3) 7.18 f 0.04(20) 7.32 f 0.02(5) 7.52(15) 5.99(3) 6.01(2) 4.95 f O.OS(l0) 4.91 f 0.02(10) 4.96(70) 4.30 f 0.03(7) 4.24(8) 3.63 f 0.03(7) 3.68(11) 3.30 f 0.02(5) 3.28(21) 3.32 f 0.02(6) 3.03 3 0.06(4) 2.97 f 0.06(2) 2.97(24)

4) d(h(I) 30.0(100) 14.72(68) 9.774(12) 7.369(5) 5.847(1) 4.881(16) 4.187(1) 3.564(4) 3.257(2) 2.923(4)

29.8 & 0.5t 1.4919 & 0.0002t 1.5057 f 0.00087 1.506 30.1 14.7 14.0, 12.3

29.39t

23.98t 14.7 14.7 32.3 f 0.5

11.9 11.7 31.6 & 0.2t

12.3 23.7 5 0.2t 31.8 O.lt 27.1

*

d(&(O 30.0(320) 15.2(240) 10.0(20) 7.557(20) 5.980(3) 5.006(70)

6) d&(O 29.4(100) 14.66(60) 9.825(2.6) 7.417(3.4) 5.905(0.2) 4.921(9.2)

3.705(20) 3.297(24) 2.954(20)

3.691(2.5) 3.271(2.4) 2.937(2.7)

7) d(.m 30.5(254) 14.98(196) 9.88(7) 7.40(24) 5.91(1) 4.93(39) 4.23(4) 3.68(17) 3.28(12) 2.94(11)

30.0 f 0.5t 1.493* 27.0 f 0.87 24.0 f 0.67

29.48 f 0.2t

29.6 f 0.4t

29.5 f 0.2t

29.5 f O.lt

* 0.2t

23.5 f 0.3t

5)

*

23.5 0.37 23.5 f 0.3t

23.3

23.797 32.197 26.847

31.9 0.8t 26.5 f 0.1

31.1 & 0.6t

23.1 f 0.2t 31.6 f 0.4t 29.6 & 0.77 26.6 0.17 30.4 & 0.2t (Continued)

*

Basal spacing: values for the X-ray powder diffraction peak occurring at the smallest glancing angle on each chart. Probability coefficients: P(A), chlorite layers; P(B), expandable montmorillonite layers. A: after boilingin 1 N KOH-1 N KCI for 5 hr. B: after boiling the K+-clay in 1 N AIC13 for 1 hr. t Mean values or corrected values. 1) the Kurata specimen from the Kurata kaolinite-type Roseki mine, Yamaguchi Prefecture (Sudo et al., 1954a). 2) the Hanaoka specimen from the Tsutsumizawa ore body of the Hanaoka mine, Akita Prefecture (Sudo and Hayashi, 1955; Hayashi, 1961). 3) the Kamikita specimen from the Honko ore body of the Kamikita mine, Aomori Prefecture (Sudo and Kodama, 1957). 4) the Niida specimen from a mineralized area of the Kuroko region at Niida, southern part of Odate, Akita Prefecture (Kimbara and Nagata, 1974). 5 ) the Takatama specimen from the Takatama mine, Fukushima Prefecture (Shimoda, 1969). 6) the Tohoo specimen from the Tohoo Roseki mine, Aichi Prefecture (Nishiyama et a/., 1975). 7) the Hokuno specimen from the Hokuno Toseki mine, Gifu Prefecture (Ichikawa and Shimoda, 1976).

c!

m w

INTERSTRATIFIED MINERALS

292

TABLE 8.5. X-Ray diffraction data of interstratified trioctahedral ch!orite/saponites

-

--

1 001

001 002 003 004 005 006 007 008 009 00,lO

-

-

001 060,331

d ( ' m 29.62(41) 14.82(60) 9.84(6) 7.39(12) 4.91(21) 4.22(4) 3.68(13) 3.27(9) 2.94(10) 29.517 1.535

300"C, 1 hr 450°C, 1 hr 600"C, 1 hr 700°C Mg-f Ca-f Na-f K-f EG 30.9 NH4N03 Mg EG Ca EG Na EG K+EG Mg GL Ca GL Na GL K+GL

+

+ +

+

+ +

2

d(A)(Z) 29.4(8) 14.8(20) 9.8(3) 7.38(5) 5.81(1) 4.90(8) 4.23 ? 3.63(6) 3.30(3) 2.94(4) 29.7 1.54

3

d(A)(Z) 31.08(18) 14.92(100) 9.752(6) 7.308(24) 5.901(3) 4.806(12) 4.259( 1) 3.633(19) 3.264(2) 2.915(6) 29.55t 1.542

4

d(A)(Z) 29(5) 14.6(40) 9.61(2) 7.24(5) 4.83(9) 3.61(7) 3.28(2) 2.898(3)

5

d(W)(Z) 29.3 14.7 9.78 7.36 5.879 4.904 4.199 3.676 3.268 2.940

14.82 9.927 7.369 4.897 3.669

14.82

13.38 23.817 23.857 24.507

11.78 12.27

28

30.5

6

d(A)(Z)

28.9 29.4 26.7, 29.4 26.7

31.427 27.377

16.35 12.80 32

31.4 31.0 31.2 31.4 28.8 32.1 32.5 28.3

Basal spacing: values for the X-ray diffraction peak occurring at the smallest glancing angle on each X-ray chart. 7 Mean values or corrected values. Mg-f, etc.: saturated with magnesium ions, etc. EG: Ethylene glycol. Mg-EG, etc: saturated with magnesium ions and successively treated with ethylene glycol, etc. GL: Glycerol. 1) the Tsunemi specimen from the Tsunemi mine, Fukuoka Prefecture (Takahashi, 1959). 2) the Noto specimen from the Noto Kuroko-type gypsum mine, Ishikawa Prefecture (Sugiura, 1962). 3) the Yarnakata specimen from the Green Tuff, Yamakata district, Ibaragi Prefecture (Kimbara et a/.,1971). 4) the Wanibuchi specimen from the Wanibuchi Kuroko-type gypsum mine, Shimane Prefecture (Shirozu et al., 1975). 5) the specimen found in quartz veins in dolomitized recrystallized limestone at Kasuga-mura, Gifu Prefecture (Suzuki et al., 1974). 6) the Nibetsu specimen found in the pillow lavas of the Sunakobuchi Formation (Miocene) distributed in the western part of Taiheizan, Akita Prefecture (Kimbara and Shimoda, 1972).

MINERALOGICAL PROPERTIES

293

interstratified mineral composed of 45 % chlorite and 55 % saponite-like layers. Some of the minerals having about a 14.8 A reflection and its higher orders are considered to be randomly interstratified chlorite/montmorillonite, such as the Nibetsu specimen. However, in the case of some of the minerals, the structures and properties of the elementary layers are clearly more complicated and similar to those of so-called swelling chlorite (Shimoda, 1974a). B. Differential thermal analysis

As shown in Fig. 8.6, the DTA curves of the regular or almost regular interstratified minerals may be divided into three types according to their endothermic and exothermic temperatures. These temperatures are also closely related to the chemical compositions of the minerals. The Takatama specimen, which consists of interstratified dioctahedral chlorite/montmorillonite,undergoes dehydroxylation of the silicate and gibbsite layers at about 550°C. The exothermic peak related to recrystallization appears at about 1OOO"C. The curve resembles that in the case of the specimens described by Kanaoka (1968, 1974). The curves for the Tohoo (Nishiyania et al., 1975) and Hokuno specimens (Ichikawa and Shimoda, 1976) are also the same, although they contain small amounts of lithium, The shoulder at about 650°C in the specimens described by Kanaoka (1968, 1974) and by Ichikawa and Shimoda (1976) may be ascribed to dickite as an impurity. The Kamikita specimen, which is composed of di,trioctahedral chlorite and

500 Temp. ("2)

Fig. 8.6. DTA curves of interstratified chlorite/montmorillonites. T : the Takatama specimen (Shimoda, 1969). K : the Kamikita specimen (Sudo and Kodama, 1957). No: the Noto specimen (Sugiura, 1962). Ni: the Nibetsu specimen (Kimbara and Shimoda, 1972).

294

INTERSTR4TIFIED M INERALS

montmorillonite, exhibits an endothermic peak at about 600°C. This temperature is thus slightly higher than that in the Takatama specimen. The exothermic peak appears at about 1080°C. A small but clear endothermic peak can be recognized at about 900"C, but it is uncertain whether this peak is related to dehydroxylation of the silicate layers or not. The silicate layers of this mineral are considered to have a dioctahedral structure as montmorillonite, although the Takatama specimen shows no endothermic reaction in the same temperature range, in spite of the fact that its silicate layer is dioctahedral. A specimen from the Iwami mine, Shimane Prefecture, described by Shimoda (1975) also yields a curve with similar properties. The Noto specimen, which is an interstratified trioctahedral chlorite/saponite (vermiculite), undergoes dehydroxylation of the brucite layer at about 620°C and that of the silicate layer at about 850°C. These temperatures are closely similar to those of trioctahedral chlorite. The Nibetsu specimen, which is composed of trioctahedral chlorite and saponite, exhibits a double endothermic peak between 500 and 700°C. Since ironrich saponite generally shows endothermic reactions at about 550 and 850°C (Yoshimura et af., 1975; Kimbara and Honda, 1975), the peak at the lower temperature is considered to be related to saponite and the higher one to chlorite. The endo- and exotherniic peaks between 800 and 900°C are ascribed to the endothermic reaction of saponite and the exothermic reaction of chlorite, respectively, C. Chemical analysis

Chemical analyses of the interstratified minerals have been reported by many authors, although the pure mineral appears to be. rare in nature. Some of the data are listed in Table 8.6 and 8.7, and the structural formulae based on a negative charge of SO( =Oao(OH)io) are also shown. Chemical analysis of the Takatama specimen revealed a negligible amount of MgO, indicating that the two octahedral sites of the chlorite component are dioctahedral. The Kurata specimen, which was first described by Sudo et al. (1954a,b) as an interstratified dioctahedral chlorite/montmorillonite, also lacks any significant MgO, although it contains a small amount of kaolinite as impurity. The Taniyama and Uebi specimens described by Kanaoka (1968) contain very small amounts of MgQ and also consist of interstratified dioctahedral chlorite/montmorillonite. Kanaoka (1974, 1975) later showed that most interstratified chlorite/montmorillonites occurring in the so-called Toseki deposits are composed of dioctahedral chlorite and montmorillonite. Nishiyama et al. (1975), and Ichikawa and Shimoda (1976) discovered a variety of this mineral containing appreciable amounts of lithium in certain Roseki and Toseki deposits. Such material was first reported from Huy, Belgium, by Brown et al. (1974). However, it is not sure whether these minerals are interstratified cookeite/montmorillonite or not.

TABLE 8.6. Chemical analysis of interstratified dioctahedral chlorite/montmorillonites 1) 2) 3) Chemical composition (%) 37.25 39.94 SiOz 49.2-65.3 0.74 Ti02 0.06-0.50 30.69 33.17 A1203 24.1-47.8 4.55 1.34 Fez03 0.62-1.42 0.25 0.18 FeO tr MnO 1.35 6.44 MgO 0.02-0.71 1.18 1.30 CaO 0.09-0.3 1 0.52 NazO 0.09-0.49 2.15 0.24 KzO Liz0 HzO(4-I 8.60-12.41 18.10 11.64 HzO(-) 0.29 4.39 S 5.38 0.69 pZo5 0.08 Si:O -0.26 Total 100.41

]

Structural formula (Ozo(0H)io) Si

AW) AWI) Fe3f Fez+ Mn Mg Ti Li Ca Na K Note: Numbers 1-7 correspond to those in Table 8.4.

4)

5)

6)

7)

36.96 0.34 32.09 1.57 tr n.d. 8.20 2.21 0.16 0.23

42.14

41.60

37.38 0.30

36.40 1.82

44.20 tr 36.65 1.24

0.08 1.65 0.15 1.40

12.71 6.12

11.22 6.16

0.29 0.38 0.14 0.38 1.04 11.12 6.87

100.48

100.04

0.54 2.56 0.12 0.58 0.60 (Ig. loss) 11.54 1.97

n.d. 100.59

100.00

6.65 1.35 5.16

6.26 1.74 4.65 0.20

6.86 1.14 6.025 0.035

6.80 1.20 5.795 0.225

69.15 1.085 5.67 0.145

1.595

2.07

0.02

0.07

0.125

0.23 0.17 0.05

0.40 0.05 0.05

0.285 0.045 0.29

0.68 0.065 0.045 0.08

0.38 0.43 0.045 0.115

INTERSTRATIFIED MINERALS

296 TABLE 8.7.

Chemical analysis of interstratified trioctahedral chlorite/saponites 1) Chemical composition (%) SiOz 39.46 TiOz 0.02 A1203 12.59 Fez03 0.31 FeO 0.14 MnO Mi@ 24.91 CaO 0.06 NazO 0.22 KzO 0.03 HzO(S-) 11.20 HzO(-) 10.94 pzo5 Total 99.88

E

2)

3)

4)

5)

33.95 tr 19.20 0.71 0.69

34.33

41.16 0.16 12.55 1.03 6.05

26.31 0.70 0.74 0.05 11.26 6.55

35.95 0.30 15.13 6.65 9.15 0.38 14.76 1.86 1.13 1.13 7.30 6.62

100.16

100.00

99.77

14.94 0.15 0.63 0.04 32.19 0.33 0.11 0.20 13.18 3.67

EC NazO

Structural formula (OZO(OH)IO) Si 7.09 At (IV) 0.91 A1 (VI) 1.76 Fe3f 0.04 Fez+ 0.02 Mn Mg 6.67 Ca 0.04 Na 0.08 K 0.01 EC: Exchangeable cations. Note: Numbers 1-6 correspond to

6) 36.7 0.1 9.1 10.6 2.3

0.05

25.67 1.85 0.26 0.03 7.95 3.17 0.08 100.01 0.37 1.34

21.7 2.2 0.4

0.2 8.1 9.5 100.9

0.05

0.03 5.90

2.10 1.83 0.09 0.10 6.81 0.26 0.25 0.01

6.37 1.63 1.56 0.90 1.37 3.94 0.36 0.39 0.26

6.16 1.84 1.32 0.02 0.10 0.00 8.60 0.06 0.04 0.04

those in Table 8.5.

Interstratified minerals having a di, trioctahedral chlorite component have been found in the alteration areas of some Kuroko deposits. The Kamikita specimen contains 6.44% MgO and the chlorite component is di,trioctahedral. A mineral from the alteration area of the Niida Kuroko-type mineralized area is also composed of di,trioctahedral chlorite containing 8.2 % MgO (Kimbara and Nagata, 1974). The Noto specimen includes 26.13 % MgO and the structural formula indicates that the mineral is an interstratified mineral composed of trioctahedral chlorite and saponite. The minerals found in the so-called Green Tuff usually contain ferric and ferrous iron. The Nibetsu specimen has a high content of

MINERALOGICAL PROPERTIES

291

Fe203, and an almost regular mineral from amygdales in an andesite tuff breccia in the Taiheizan district, Akita Prefecture, also has 7.17% Fez03 and 7.22% FeO (Kimbara, 1975). The minerals found in amygdales appear to be characterized by the presence of abundant of iron oxide. The Gokan specimen from Tertiary green sand contains 6.95% Fez03 and 16.09% FeO, and the amount of MgO is very low. Although this specimen includes iron-rich chlorite as an impurity, its chemical composition is clearly different from the other minerals. The interstratified mineral in the Gokan specimen seems to be composed of an iron-rich chlorite such as thuringite or ripidolite, and nontronite. In Japan, most interstratified dioctahedral chlorite/montmorillonites occur in Toseki and Roseki deposits and they usually contain small amounts of KzO and NazO. Interstratified minerals having a di,trioctahedral chlorite component have been found in the alteration areas of some Kuroko deposits. Although the chemical compositions of the dioctahedral and trioctahedral minerals apparently form a continuous series, it is difficult to discuss and interpret the compositions on the same basis as the mineralogy. The origins and mineralogical properties of the specimens are essentially different. D . Infrared absorption analysis

The infrared absorption data of the interstratified dioctahedral and trioctahedral minerals with a regular sequence may be grouped into three types on the basis of the frequency values of the OH vibrations and the bands ascribed to the Mg(A1)-OH vibration in the range, 750-650 cm-l. These frequencies are closely related to the chemical compositions. As shown in Table 8.8, the minerals having dioctahedral chlorite and di,trioctahedral chlorite components exhibit almost the same three absorption bands in the range, 3400-3700 cm-l. The three bands appear at about 3630, 3540 and 3390 cm-l. The 3630 cm-1 band persists up to 7OO0C,but the band at 3450 cm-l disappears at 500" C. The former band may therefore be ascribed to the OH stretching in the silicate layer, and the latter appears to be ascribable to the OH stretching in the hydroxide layer. The Noto specimen, which is composed of trioctahedral chlorite and saponite, has the band of OH stretching of the silicate layer at 3690 cm-l. This band position corresponds to those in saponite and talc. The OH stretching of the hydroxide layer appears at 3592 cm-l. The minerals containing abundant iron oxide usually show no clear absorption bands in the range, 3400-3700 cm-l. The Nibetsu specimen exhibits an absorption band at 3400 cm-1 with a shoulder at 3550 cm-l. The almost regular interstratified mineral described by Kimbara et al. (1971), which contains 6.47 % Fez03 and 8.90% FeO, gives only one absorption band at 3560 cm-l in this range. The Si-0 vibration bands of the minerals appear at about 1000 and 500 cm-l. These bands occur in similar regions and there is no detectable difference be-

298

INTERSTRATIFIED MINERALS

TABLE 8.8. Infrared absorption band frequecnies of interstratified chlorite/montmorillonites Takatama

Kamikita

3670 Inf 3640 S

3630 S

3545 s

3540 S

Noto 3690 M

3592 S 3420 S,B

3390 S, B 1640 M 1404 W 1055 Sh 1035 S, B

Nibetsu

3550 Sh 3400 S

3380 S, B 1635 M 1080 Sh 1050 Inf

1055 Sh

1030 S, B 1012 S, B

950 Inf 820

w

940 Inf 827 W

963 Sh

997 S, B 950 Sh

760 W 750 S 735 Sh 705 Sh

704 S

612 S 650 S 630 Sh 544 s 523 Sh

540 S

510 Sh

478 s 475} 455

s

465 S

435 s 415 M 408 S Takatama (Shimoda, 1969). Kamikita (Sudo and Kodama, 1957). Noto (Sugiura, 1962). Nibetsu (Kimbara and Shimoda, 1972). The IR data for the Takatama, Kamikita and Noto specimens are from Shimoda (1975). S: Strong. M: Medium. W: Weak. Sh: Shoulder. Inf: Inflection. B: Broad.

tween the interstratified minerals composed of dioctahedral or di,trioctahedral chlorite and montmorillonite, and those composed of trioctahedral chlorite and saponite. As seen from the data for the Nibetsu specimen, the effect of iron substitution may contribute to a slightly lower frequency for the band, but the specimen described by Kimbara et al. (1971) has a band at 1005 cm-1 with a shoulder at 1085 cm-I, which is a broadly similar pattern to the Noto specimen. The minerals also exhibit a band ascribable to the Mg(A1)-OH vibration in the range, 750-650 cm-l. The wave numbers of the bands are related to the respective chemical compositions. In the Takatama specimen, the band appears at

MINERALOGICAL PROPERTIES

299

750 cm-l. On heating at 500"C, this band is lost and a weak band appears at 730 cm-l. The 730 cm-l band persists up to 700°C. The 750 cm-l band is related to the A1-OH vibration in the hydroxide and silicate layers. In the Taniyama and Uebi specimens described by Kanaoka (1968), the band also appears at 750 cm-l. The Kamikita specimen has the band at about 700 cm-l. It is clearly recognizable after heating at 500°C but disappears at 700"C, and a very weak band appears at 718 cm-l at 700°C. In the Noto specimen, the band is at 672 cm-l and it persists up to 700°C. This band in the Noto specimen resembles those in saponite and trioctahedral chlorite. The band in the minerals containing ferric and ferrous iron shifts to lower frequencies. The Kamikita specimen contains di,trioctahedral chlorite in its structure, but the band is not a mixture of the Al-OH vibration in the silicate layer and the Mg-OH vibration in the hydroxide layer. It appears at an intermediate position between the two. The reason for this is not clear, although the bands of di,trioctahedral chlorites also appear in an intermediate position (Shimoda, 1975). E. Electron microscopy

Electron micrographs of the Takatama specimen show an aggregate of thin

Fig. 8.7. The Takatama specimen.

300

INTERSTRATIFIED MINERALS

Fig. 8.8. The Noto specimen.

Fig. 8.9. Lattice image of the Nibetsu specimen (Akai, 1975).

MINERALOGICAL PROPERTIES

301

flakes (Fig. 8.7), while the Noto specimen appears as thin and smooth particles (Fig. 8.8). Akai (1975) has observed the lattice image of the random interstratification in the Nibetsu specimen, as shown in Fig. 8.9. 8.2.3. Interstratijied kaolin/montmorillonite

I

The occurrence of interstratified kaolin-montmorillonite was first described by Sudo (1956) and Sudo and Hayashi (1956). Shimoyama et al. (1969) later studied the mineralogical properties of this mineral. Takeshi et 01. (1969) and Takeshi and Uno (1971, 1974) also reported the occurrence of the mineral in socalled acid clay. Shimoda and Kohyama (1971), Kohyama and Shimoda (1974), Tsuzuki and Sat0 (1974), and Sat0 et al. (1974) studied the minerals and demonstrated the possibility of the existence of an interstratified structure between kaolin and montmorillonite components. Many investigators in other countries have also reported the occurrence and mineralogical properties of such minerals (Altschuler et al., 1963; Schultz et al., 1971; Wiewiora, 1971, 1972). A. X-Ray diffraction data

X-Ray diffraction patterns for these minerals may be ground into three types: (1) patterns similar to a kaolin, (2) patterns similar to montmorillonite, and (3) patterns with a very weak and broad reflection between 7 and 15 A, which sometimes disappears completely. A mineral having no clear reflections other than hk reflections was first reported by Sudo (1956) and Sudo and Hayashi (1956a). The specimens were found in the Raimaru, Wake, Tsuruoka, Nata and Awazu clays, which are representative “acid clays” in Japan, and the Awazu specimen was studied critically. As shown in Fig. 8.10A, it gives no basal reflections, whereas the 02, 11, 13, 20 and 06,33 reflections are strong and clear. Ethylene glycol treatment causes all the reflections to be weakened but no critical changes are observed in the pattern. On heating at 300”C, a weak and broad reflection appears at about 8 A. This mineral has been considered to constitute an interstratified mineral with a structure composed of kaolin and montmorillonite layers as shown in Fig. 8.10B. The proportion of montmorillonite layers is abundant in the inner part, but at the margin the layers of kaolin increase in abundance. Tsuzuki and Sat0 (1974) demonstrated that the mineral is composed of four different layers such as kaolinite, montmorillonite, halloysite and pyrophyllite layers. The pyrophyllite layer described by them appears to be identical to the dehydrated montmorillonite layer. Shimoyama et al. (1969) obtained a specimen with a very broad reflection at about 8 A from the acid clay deposit of Nakamaruke, Niigata. As shown in Table 8.9 and Fig. 8.11, the 8 8, reflection shifts slightly to 7.6 8, after heating at 150°C, and it persists up to 450°C. A broad peak at about 11 A appearing on heating at 150°C is observed after heating at 750°C. The specimen is considered

INTERSTRATIFIED MINERALS

302

1

20'

10"

I

I

25" I

28 B K K

M

M =montmorillonite layers K = kaolin mineral layers

lo"

20"

I

I

25" I

28

Fig. 8.10. X-Ray diffraction patterns of the Awazu clay (A) and a structural model for it 03) (Sudo and Hayashi, 1956a). 1 , Air-dried natural state; 2, after treatment with ethylene glycol; 3-6, after heating at various temperatures.

TABLE 8.9. X-Ray diffraction data of the Nakamaruke acid clay (interstratified kaolin-montmorillonite) before and after heating at various temperatures for 1 hr (Shimoyama et al., 1969) Room temp. d(A) z

150°C 300°C d(A) z d(i) I 11 4.5b 10.6 6b 7.6 8 14b 7.6 10b lob 17 4.48 17 4.48 15 4.48 9 3.36 11 13 3.36 3.35 4 2.56 2.56 7 2.56 5.5 1.683 2.5 3 1.680 2.5 1.677 1.494 3.5 1.494 3.5 5 1.492 b indicates a broad reflection.

450°C Z 10.6 5b 7.7 8b 4.48 15b 3.36 11 2.56 4 1.683 2.5 1.494 2.5

d(A)

600°C d(A) I 11.4 4.48 3.36

750°C d(A) z 5b

6 12

11.0 3 ~4.48 2 3.36 13

MINERALOGICAL PROPERTIES

303

Natural sample 1

1

1

1

1

1

1

I

I

I

I

I

I

I

1

1

1

1

1

1

1

EG

300'C

I I

I

I

I

I

I

I

450%

750% I

I

10"

20"

I

30"

I

I

I

I

40"

50'

60'

70'

28

Fig, 8.11. X-ray diffraction patterns of the Nakamaruke acid clay (interstratified kaolin-montmoriIlonite) before and after various treatments (Shimoyama et a / . , 1969).

to constitute a randomly interstratified mineral with about 75 kaolin mineral and 25 % montmorillonite layers based on its chemical Composition. A specimen from the Awazu clay studied by Kohyama and Shimoda (1974) also gives a broad reflection at about 7.6 A and the pattern resembles that of halloysite rather than that of kaolinite (Fig. 8.12). The broad and weak reflection expands to 7.8 A on treatment with glycerol. After heating at 300°C, it shifts slightly to 7.7 A. After treatment with hydrazine hydrate, it moves to 10.8 A. A comparison of the observed and calculated X-ray diffraction patterns

INTERSTRATIFIED MINERALS

304

4

h10.8

2e ( c ~ K ~ )

Fig. 8.12. Observed (A) and calculated (B) X-ray diffraction patterns for the Awazu clay before and after various treatments (Kohyama and Shimoda, 1974). 1, Air-dried natural state; 2, after treatment with glycerol; 3, after heating at 300°C; 4, after treatment with hydrazine hydrate. B indicates the pattern of a randomly interstratified 75 % kaolin/25 % montmorillonite.

after such treatments indicates that the specimen is a randomly interstratified mineral with about 75 % kaolin and 25 % montmorillonite layers. A specimen from the Sakaedani acid clay gives a 16.5A reflection, the spacing of which is slightly larger than that of normal montmorillonite (Hayashi, unpublished data; Kohyama and Shimoda, 1974). The 002 reflection appears a t about 8 A. Glycerol treatment causes expansion of the two reflections to 19.2 and 8.5 A, respectively. The 16.5 A reflection shifts to 13.4 A on treatment with hydrazine hydrate. A comparison of the observed and calculated X-ray patterns indicates that the specimen has a randomly interstratified structure with about 30 % kaolin mineral and 70 % montmorillonite layers. The specimens described by Takeshi et nl. (1969) and Takeshi and Uno (1971, 1974) also give a reflection at about 16 A, and they apparently have a similar interstratified structure. B. Differential thermal analysis

DTA curves for the minerals resemble that of halloysite (Fig. 8.13). Although the X-ray diffraction patterns can be grouped into three types as mentioned, the minerals all show similar curves on DTA. The first endothermic reaction occurs between 100 and 200"C, and the second one appears between 500 and 600"C. The endothermic reaction indicating the presence of montmorillo-

MINERALOGICAL PROPERTIES

500 Temp.

(2)

305

1000

Fig. 8.13. DTA curves of interstratified kaolin/montmorillonites. A: the Awazu clay (Sudo and Hayashi, 1956a). Mi and Mz: the Mizusawa specimens (Takeshi and Uno, 1974). Specimen MI exhibits a basal reflection at about 15 A and its mineralogical properties resemble montmorillonite. However, specimen M2 is clearly different from normal montmorillonite.

nite layers is barely detectable. An endothermic peak following an exothermic peak appears at between 850 and IOOO'C, although the exothermic peak is not so sharp and strong as that given by kaolin minerals. The endothermic reaction at about 900°C is unclear in curves of specimens having no X-ray reflection such as montmorillonite. Sudo (1956) and Sudo and Hayashi (1956a) have demonstrated the presence of montmorillonite layers in the Awazu specimen by DTA using piperidine treatment, although the layers cannot be detected by X-ray analysis. This method thus appears suitable for detecting the montmorillonite component of minerals showing no basal reflections such as the Awazu specimen. c. Chemical analysis The chemical composition of the Awazu specimen has been given by Sudo and Hayashi (1956a), as shown in Table 8.10. The data indicate that the mineral is chemically an intermediate between kaolin and montmorillonite. The minerals usually contain abundant impurities such as quartz, cristobalite, and occasionally large amounts of volcanic glass. Critical discussions have thus not been made of the observed chemical compositions. However, Shimoyama et al. (1969) collected a series of specimens from typical montmorillonite to interstratified mineral from the acid clay at Nakamaruke, Niigata Prefecture. As shown in Table 8.10, the chemical composition of the mineral is somewhat different from that of montmorillonite or kaolin minerals. The percentage of SiOz decreases with increasing A1203, although the content of A1203 still re-

306

INTERSTRATIFIED MINERALS

TABLE 8.10. Chemical analysis of complicated interstratifications of kaolin and montmorillonite, and montmorillonite associated with the interstratifications

A Chemical composition( %) Si02 41.94 Ti02 0.40 A1203 30.12 Fez03 2.42 FeO 0.21 MnO MgO 1.52 CaO 0.32 NazO KzO HzO(f) 11.10 HzW-1 12.88 Pzo5 Total 99.91 Exchangeable cations Na

K

N1

N2

46.50 0.39 29.90 0.94 0.27 0.00 1.03 0.76 0.43 0.64 12.79 6.87 0.01 100.53

48.73 0.28 19.54 2.07 0.13 0.00 2.96 0.72 0.32 0.28 8.68 15.59 0.02 99.32

3.2 2.6 3.2

2.7 1.9 2.6

MI 47.68 1.92 20.03 5.45 0.48

Mz

2.48 0.24 0.38 0.24 7.96 13.52

50.08 0.47 15.78 5.34 0.01 0.14 3.51 0.90 0.29 0.44 8.53 14.46

100.38

99.95

2.3 1.2 7.3 5.3 0.7 58.3

1.1 1.1 33.4 29.4 0.6 87.0

Ca Mg Al 9.9 49.5 CEC (me/l00 g) 37.4 104.9 P K : PM 80:20* 3:1* 75:25** 76:24t Px: Kaolin mineral layers. PM:Montmorillonite layers. *Estimated from the chemical compositions (Sudo and Hayashi, 1956a; Shimoyama ei al., 1969). **Estimated from the specimens heated and/or treated with glycerol (Kohyama and Shimoda, 1974). t Estimated by Cradwick and Wilson (1972) from peak migration curves prepared by calculation with the X-ray intensity formula. A, the Awazu acid clay (interstratified kaolin/montmorillonite) from Awazu, Ishikawa Prefecture (Sudo and Hayashi, 1956). N1 and Nz, the Nakanaruke acid clays from Nakamaruke, Niigata Prefecture. N1 is interstratified kaolin/montmorillonite and corresponds to the material in Table 8.9. Nz is a sample of the montmorillonite (Shimoyama et nl., 1969). MI and Mz, the Mizusawa acid clays from Mizusawa, Yamagata Prefecture. MI is the interstratification and Ma is montmorillonjte associated with the interstratification (Takeshi and Uno, 1974).

mains lower than that of kaolin minerals. About 1 % MgO appears to be attributable mainly to montmorilloaite component. In general, the chemical compositions of the minerals are intermediate between those of montmorillonite and kaolin minerals. They are also characterized by low CEC values compared to montmorillonite. Takeshi and Uno (1974) have estimated the chemical composition of an interstratified kaolin/montmorillonite from Mizusawa, Niigata Prefecture (Table 8. lo), though it does contain some impurities.

307

MINERALOGICAL PROPERTIES D. Infrared absorption analysis

Infrared absorption data for the minerals are few and they usually involve some impurities, although Oinuma and Hayashi (1968) have given IR patterns for the Awazu, Wake and Raimaruke specimens which are almost free from impurities. These specimens exhibited bands at 3700,3625,3400(sh), 1100, 1025, 910, 790, 750, 690, 530, 467 and 430 cm-l, and the patterns are thus close to halloysite. The IR data clearly demonstrate the existence of kaolin layers in the interstratifications. Kato (1976) has also reported that a mineral having no clear basal reflections on X-ray analysis gives an IR pattern similar to that of halloysite. 8.2.4. Interstratijied micalchlorite

The existence of regularly interstratified mica/chlorite was first inferred by Cole and Neilson (195811959) in the Ordovician shales of western Victoria. Recently, Eroshchev-Shak (1970) has also demonstrated the occurrence of an interstratified biotite/chlorite in a biotite gneiss from Lithuania. In Japan, Shirozu et al. (1971) have identified an interstratified mica(muscovite)/di,trioctahedral chlorite in a wall rock alteration area of the Hanaoka mine, a typical Kuroko deposit in Japan. The mineral from the Hanaoka mine gives a reflection at 24.2 A and its higher orders (Table 8.1 1). These basal reflections are close to an integral series but show slight changes after treatment with ethylene glycol and heat. Shirozu et al. (1971) therefore concluded that this mineral is an almost regular interTABLE 8.1 1. 001 spacings and structure factors of interstratified mica/di,trioctahedral chlorite from the Hanaoka mine (Shirozu and Higashi, 1976) ___-

I 1 2 3 4 5 6 7 8 9 I0 11 12 13 14 15

d(A) 24.2 12.36 8.01 6.09 4.83 4.02 3.47 3.01 2.687 2.406 2.190 2.017 1.860 1.723 1.602

~ooI(A) 24.2 24.72 24.03 24.36 24.15 24.12 24.29 24.08 24.18 24.06 24.09 24.20 24.18 24.12 24.03

IFIobs

4.7 28.4 44.4 23.7 89.3 38.3 109.9 53.0 49.7 10.4 20.5 93.5 34.9 13.0 19.3

Fcaic 6.8 -29.7 -42.7 22.7 -88.4 40.4 -108.9 -52.6 47.5 -8.8 20.1 91.1 37.1 -14.2 19.4

I 16 17 18 19 20 21 22 23 24 25 26 27 28 29

d(W)

d~ol(A)

-

-

1.419 1.2697 1.2068 1.1482 1.0515 1.0059 0.8926 0.8610 0.8319

24.12

I FI obs 52.1

24.12 24.14 24.11

26.5 41.5 23.4

-

-

-

-

24.18 24.14

14.1 37.5

-

-

-

-

24.10 24.11 24.13

42.8 13.9 15.3

Fcslc

3.8 -51.5

6.6 22.9 41.7 -26.4 -1.3 -16.9 37.8 -0.9 -3.9 -41.8 18.3 11.9

308

INTERSTRATIFIED MINERALS

stratified mica/chlorite with a small amount of randomly intermixed expandable layers. However, the spacing of the basal reflections and the Fourier synthesis curve (Fig. 8.14) seem to suggest that the mineral is of almost regular type. The DTA curve shows an endothermic peak at about 600°C and a small exothermic peak at about 950°C (Fig. 8.15). The curve is similar to those for

Fig. 8.14. One dimensional Fourier synthesis curve for an interstratified mica-di,trioctahedralchlorite from the Hanaoka mine (Shirozu et al., 1971).

U

W

~

260

3bO.

4-J

500

600

700

800

SvJ

1buO

1

Fig. 8.15. DTA curves of interstratified mica-di,trioctahedral chlorite, and di,trioctahedralchlorite. (Shirozu et al., 1971). 1) An interstratified mica-di,trioctahedral chlorite. 2) Di,trioctahedral chlorite containing a small amount of an interstratified mica-di,trioctahedralchlorite.

MINERALOGICAL PROPERTIES

309

di,trioctahedral chlorites given by Hayashi and Oinuma (1964) and Tsukahara (1964). The infrared spectrum of the mineral also resembles that of di,trioctahedral chlorite (Hayashi and Oinuma, 1964). The chemical composition and structural formula indicate that the mineral is composed of mica (muscovite) and di, trioctahedral chlorite (Table 8.12). TABLE 8.12. Chemical analysis of interstratified mica/di,trioctahedral chlorite and di,trioctahedral chlorite (Shirozu ef al., 1971)

Na2O KaO LiO HzO(+) HaO(-)

9.90 0.07 0.10 3.42 none 10.54 1.20

2) 35.69% 0.62 35.81 0.07 0.07 11.86 0.03 0.15 2.77 none 11.46 1.39

3) 39.3% 0.8 37.7 0.0 0.0 7.7 0.1 0.0 4.0

Total

100.78

99.92

100.0

1)

SiOz Ti02 A1203

FeO MnO MgO CaO

1) 2) 3) 4)

37.72% 0.70 37.05 0.04

0.04

-

Si Ti A1 Fe

4) 6.13 0.09 6.90 -

Mn

-

Mg Ca Na K

1.79 0.02

-

0.80

9.4 1 .o

Interstratified mica/di,trioctahedral chlorite containing 25 % di,trioctahedral chlorite. Di, trioctahedral chlorite containing 30% of an interstratified mineral. Interstratified mica/di,trioctahedralchlorite (values after correction for impurities). Cation numbers of the interstratified mineral.

Shirozu and Higashi (1976) have restudied the crystal structure by X-ray analysis and shown that the reflections may be indexed on the basis of an orthohexagonal cell with b = 9.024 and c = 24.14 A. They also indicated that the mineral has a structure with a stacking sequence composed of 1M or 2M1 mica and IIb chlorite layers.

8.2.5. Stevensite showing an interstratijication by dehjidration Stevensite was regarded by Faust and Murata (1953) as a species of the montmorillonite group. However, Brindley (1955) identified an interstratified structure composed of talc-like and saponite-like layers in stevensite. Faust et al. (1959) also detected a reflection at about 24-26 A and demonstrated that stevensite has a defect structure caused by a deficiency of octahedral cations. The portion with the deficiency of octahedral cations is montmorillonite-like and the portion without the deficiency is talc-like. Alietti (1956) reported the occurrence of a regular interstratified talc/saponite from Monte Chiaro, North Italy, and Veniale and van der Mare1 (1969) proposed the name “aliettite” for the mineral. In Japan, Otsu et al. (1963) first reported the occurrence of a simi-

310

INTERSTRATIFIED MINERALS

lar mineral in the so-called "Shiro-ishi" of the Kaminomata ore body, Obori mine, Yamagata Prefecture. Investigations by Otsu and Yasuda (1964) revealed several kinds of interstratified structures during dehydration. Later, Shimoda (1971) also found a species of stevensite with an interstratified structure by dehydration. The mineral described by Shimoda (1971) gives a reflection at 15.5 8, and its higher orders. As shown in Table 8.13, the 15.5 8, peak expands to 17.5 8, on treatment with ethylene glycol, just as montmorillonite. On heating to lOO"C, the 15.5 8, reflection shifts to 10 A, but the mineral quickly rehydrates and a new reflection appears at about 25 A (Table 8.14). The 25 8, reflection disappears on heating at 200"C, but a weak and broad reflection appears at about 25 8, after 1 week. The Fourier transform indicates a stable form for the mineral at room temperature and about 40 % relative humidity, as an interstratified structure with 44 % dehydrated and 56 % hydrated layers. The DTA curve exhibits four endothermic peaks at about 135, 600, 795 and 840°C (Fig. 8.16). The results are similar to those for stevensite (Faust and Murata, 1953) and for interstratified talc/saponite (Veniale and van der Marel, 1968, 1969). The chemical composition, as shown in Table 8.15, agrees with that of stevensite. The structural formula indicates a, deficiency of cations in the octahedral positions. The infrared spectrum resembles those of talc, saponite, hectorite and interstratified talc/saponite, as shown in Table 8.16. The spacing and intensities of the basal reflections vary according to humiTABLE 8.13. Lattice spacings, d(001), of the Obori specimen, stevensite and an interstratified talc/saponite (Shimoda, 1971) Condition of minerals Untreated G 1ycerol Ethylene glycol Water K+ 100°C 350°C 400°C 550°C

1)

d(O0 1)A

15.5t'(25ir)t2 18.0 17.5 22.0 b 11.3 10t4 10 10 9.5

2) d(OOl)A 24-25w, ir 17.7 irt3 16.7 ir 25.0 ir 19 w, ir 19 w, ir 19 w, ir

3) d(O01)A 24.5-26.5w, ir

4) d(O01)A 23.8 27.7

16.9 28.4 21.3 9.5 9.3

1) The Obori specimen (Shimoda, 1971). 2,' Stevensite (Brindley, 1955). 3) Stevensite (Faust et al., 1959). 4) An interstratified mineral of talc and saponie (Veniale and van der Marel, 1968). w: Weak reflection. b: Broad reflection. ir: shows an irrational series of basal reflections. t1 Obtained at room temperature and about 70% relative humidity. t z Obtained at room temperature and about 40% relative humidity. t 3 One complex with glycerol showed a clearly defined spacing of 26 A. t4 Quickly rehydrates and shows a reflection at about 25 A.

MINERALOGICAL PROPERTIES

311

TABLE 8.14. X-Ray diffraction data of hydrated and dehydrated Obori specimens (Shimoda, 1971)

-

1) d(A) I

15.8

2) d(A)Z 23.8 180 13.8 570

3) d(A)

4) d(A)

21.5

I 192

25.2

13.1

570

13.3

300

5) d(A) 26.3

I 75

560

12.4

240

Z

6) d(A) Z 26.8

7) __ d(A) I

65

968 12.4 190 10.0

8.1 5.21 4.57

10 36 3

4.92

12

8.6 4.95

3.49 3.28 3.08

9 10 15

3.55 3.36 3.10

7 16 9 9 20

4.92

17

3.14 40 3.14 18 All data were determined at room temperature and about 40% relative humidity.

183

5.03

14

3.23

20

1) Obori stevensite dried in air for 30 min, after saturation with water. 2) dried for 45 min after the treatment. 3) dried for 1 hr after the treatment. 4) dried for 24 hr after the treatment. 5) cooled in air for 30 rnin after being heated to 100°C for 1 hr. 6) cooled in air for 10 min after the heat treatment. 7) heated to 100°C for 1 hr.

0.0 TG

10.9

I

1

I

1

I

1

I

I

I

I

13.3 16.4

(%I

1

1

200

1

I

400 600 Temp. ("C)

I

1

aoo

1

Fig. 8.16. DTA, TG and DTG curves for the Obori specimen (Shimoda, 1971).

312

INTERSTRATIFIED MINERALS

TABLE 8.15. Chemical analysis of the Obori specimen, stevensiteand an interstratified talc/saponite (Shimoda, 1971) 1) 2) 3) Chemical composition (%) SiOz 52.76 57.30 49.42 Ti02 0.21 A1203 tr none 4.97 Fez03 0.38 0.32 4.81 FeO 1.54 28.56 MgO 23.67 27.47 MnO 1.57 0.21 tr CaO 2.19 0.97 0.60 NazO 0.37 0.03 0.38 KzO none 0.03 0.04 HzO(+) 6.52 7.17 8.35 HzO(-) 12.38 6.69 pzo5 0.03 Total 99.84 100.19 98.91 Structural formula (OZO.OO(OH)~.OO) Si 8.01 8.00 6.96 Al 0.90 Fe3f 0.14 Fe4+ 0.04 0.04 0.20 Fez+ 0.18 Mg 5.31 5.76 5.60 0.012 Mn 0.20 0.04 Mg 0.36 Ca 0.04 0.30 Na 0.10 0.02 CEC (me/ 1OOg) 41.0 36.0 37.4 1) Obori specimen (Shimoda, 1971). 2) Stevensite (Faust and Murata, 1963). 3) An interstratified mineral of talc and saponite. The specimen contains about 10% chrysotile as an impurity. The formula was calculated after correction for the impurity (Veniale and van der Marel, 1968).

dity, and the reflections obtained at room temperature and about 70% relative humidity are close to those of montmorillonite. On heating at 100 and 2OO0C, the specimen loses its interlayer water reversibly, and shows interstratifications. It is not clear whether the mineral is actually an interstratified mineral, although it does not appear meaningful to propose a definite interstratified structure for it due to the continuous humidity-dependent variation.

8.3 ORIGIN OF INTERSTRATIFIED MINERALS

The origin of interstratified minerals has been studied by many workers (Cole and Hosking, 1957; Sudo et al., 1962; Brindley and Sandalaki, 1963;Tettenhorst

ORIGIN OF INTERSTRATIFIED MINERALS

313

TABLE 8.16. Infrared absorption band frequencies of the Obori specimen and some related minerals (Shimoda, 1971) 2) ___

3685 M

3675 S

3) 3675 M

3678 S

1

3435 M 2355 W 1630 W 1435 W

1630 W

1010 s

1040 Sh 1010 s

1030 S

shJ

708 668 M

670 S

I

515 Sh

525 Sh

462 Sh 450 S

470 S 450 Sh

___-

1010 s 782 Sh

800 W

3680 S 3630 Sh 3400 S B 3200 Sh 2355 W 1630 W 1430 W 1105 Sh 1058 Sh 1004 S 800 w 693 Sh

668 S

4631 4471 436

420

1645 M

1010 s 805 W 665

655 M 611 W 530 W

614 W 528 W

3640 M 3450 M, B

520 Sh 463 S 420 Sh

1) The Obori specimen. 2) The same, after being heated to 500°C for 3 hr. 3) An interstratified mineral of talc and saponite (Veniale and van der Marel, 1969). 4) Talc (Oinuma and Hayashi, 1968). 5) Saponite (Veniale and van der Marel, 1969). 6) Hectorite from California (Ward's mineral standard H34). S: Strong. M: Medium. W: Weak. B: Broad. Sh: Shoulder.

and Johns, 1966), but no final conclusions have yet been made. In particular, studies on interstratified chlorite/montmorillonite are few (Matsuda and Henmi, 1973; Tchikawa and Shimoda, 1976; Wyart and Sabatier, 1967). The origin of the minerals has been considered essentially on the basis of their geological and mineralogical properties, although data on the synthesis and transformation of the minerals by chemical means are also important in relation to the determination of their origin (Ueda and Sudo, 1966; Tomita and Sudo, 1968a,b). 8.3.1. Interstratified mica/montmorillonite

Shutov et al. (1969) have described the formation of interstratified mica/ montmorillonite by diagenesis. However, there is no report of such an occurrence in Japan. The data of Yoshimura (1971) appear.to resemble]those of Shutov et al. (1969). Shimoda (1971) has demonstrated a transformation from biotite to interstratifications by weathering, based on the mode of occurrence and mineralogical properties of the minerals. Thus, the origin of these minerals is generally studied from geological evidence such as of diagenesis and weathering.

314

INTERSTRATIFIED MINERALS

Sudo and his co-workers showed that interstratified mica/montmorillonite occurs in the transition area between the mica and montmorillonite zones of certain Kuroko deposits (Sudo et al., 1961; Hayashi, 1961; Sudo, 1968). Sudo et al. (1962) investigated some interstratified minerals from diaspore-pyrophyllite deposits and gave mineral distribution maps for the Yonago mine, Nagano Prefecture. The maps indicate that interstratified mica/montmorillonite is closely associated with diaspore and pyrophyllite. In the report, they classified the modes of occurrence of the interstratified minerals associated with epithermal ore deposits as follows: (1) those in transitional zones between two adjacent alteration halos, (2) those in lenticular vein-shaped masses in alteration areas, (3) those filling the interspaces of ore minerals, and (4) those in areas of silica enrichment. They considered that all these mineral locations had been subject successively to different chemical conditions and that the interstratified minerals originated from previously existing mica under the influence of the changes in chemical conditions. For the formation of an interstratified structure, it is assumed that the mica must have a polar character resulting from different distributions of Si and A1 cations in each tetrahedral layer, and that it is constructed from polar layers stacked one upon the other so that the polar structures tend to join to form nonpolar units by twinning. Chemical attack may produce alterations at intervals of one layer. If the twinning is regular, the mica changes to a regularly interstratified mineral, and if it is non-regular, it changes to a randomly interstratified mineral. Sudo et al. thus assumed the existence of polarity in the structure of mica and demonstrated the mechanism of transformation from mica to interstratifications. Later, Tettenhorst and Johns (1966) also showed the polar character of montmorillonite by the Fourier transform method. Based on DTA, Cole and Hosking (1957) predicted the direction in which the transformation of the interstratified mineral would take place. They demonstrated that the dehydroxylation temperatures of the minerals may be grouped into two series (Series 1, 500-600°C; and Series 2, 6O0-70O0C), and that the relative sizes of the peaks between 500-700°C are independent of the ratio of mica to montmorillonite layers. They attributed the main endothermic peak in Series 1 to an “abnormal” montmorillonite and that in Series 2 to an “abnormal” illite, and suggested that the difference between these two series may indicate whether a mica-to-montmorillonite or a montmorillonite-to-mica transformation is occurring. Subsequently, Shimoda et al. (1969a,b) reported that the interstratified minerals formed from montmorillonite exhibited two endothermic peaks between 500 and 700”C, and that the minerals transformed from mica gave a single endothermic reaction between 500 and 600°C. Shimoda and Brydon (1971), and Shimoda and Kohyama (1971) have examined the IR properties of the layer components of the interstratified minerals. They found that the minerals formed from mica show the IR properties of mica, whereas the minerals formed from montmorillonite show those of mica and montmorillonite.

ORIGIN OF INTERSTRATIFIED MINERALS

315

The interstratified mica/montmorillonites described in the literature generally show an appreciable substitution of A1 for Si in the tetrahedral positions. The AI/Si ratio in the tetrahedral positions also indicates the direction in which the transformation was occurring. The ratio for minerals produced from montmorillonite is lower than that for minerals produced from mica (Shimoda et al., 1969a,b; Shimoda, 1972; Shimoda et al., 1974). Iiyama and Roy (1963) synthesized an interstratified mineral from gel under high pressure and temperature. However, no other reports of synthesis from gel have been given. Matsuda and Henmi (1974) synthesized interstratified mica/ montmorillonite and chlorite/montmorillonite from kaolin by the addition of various cations under a pressure of 1 kb at 300-550°C. Artificial transformations of minerals to interstratifications have been examined by many investigators (Ueda and Sudo, 1966; Tornita and Sudo, 1968a,b, 1971; Ishikawa and Shimoda, 1974; Shimoda et al., 1974). Ueda and Sudo (1966) first succeeded in transforming a mica to an interstratified mineral with a 25 A reflection under a pressure of 60-120 atm at 250-300°C. Tomita and Sudo (1968a,b) obtained an interstratified mineral from a preheated mica by acid treatment. Studies on the transformation of mica by NaTPB and LiNO3 have also been made by many investigators (Shimoda, 1971; Tomita and Sudo, 1971; Shimoda et al., 1974, Ishikawa and Shimoda, 1974). Shimoda et al. (1974) converted a mica to an expandable structure with a spacing of 14.9 8, by treatment with LiN03. The 14.9 A reflection is not expanded by ethylene glycol treatment, but the higher orders are modified to give a n irrational series. On treatment of the material with the 14.9 A spacing with KOH-KC1 solution, it changed to an interstratified structure having a reflection at about 24 A. This suggests that the silicate layer of the mica used was probably composed of two layers with different properties, one readily absorbing K+ and the other not. An expandable material formed from a 1M mica was found to absorb K+ in the interlayer position, and it changed to a random interstratification. On the other hand, material obtained from a 2M mica changed to an almost regular type. Based on the various geological and mineralogical data for interstratified mica/montmorillonites given in the literature, the variations in properties may be divided into two trends: “A” and “B”. The principal factors giving rise to these different trends appear to indicate a difference in mode of origin. That is to say, “A” is a product of a transformation process from montmorillonite to mica, while “B” is a product of the reverse process. The relation between “A” and “B” is illustrated in Fig. 8.17, based on the chemical compositions. “A” tends to show the characteristics of mica and montmorillonite, whereas “B” tends to show the characteristics of mica only, as revealed from the infrared absorption spectra (Shimoda and Brydon, 1971; Shimoda and Kohyama, 1971), DTA (Shimoda et al., 1969a,b) and the X-ray behavior (Shimoda et al., 1969b; Tomita and Dozono, 1974; Shimoda et al., 1974).

INTERSTRATIFIED MINERALS 0

f

0.1

Abnormal rnontmorillonite

0.2

0

0

0

0

I

0.3

0.333

AI/Si in the tetrahedral sheet

Fig. 8.17. Relation between the interlayer cations and AljSi ratio in the tetrahedral positions of mica, interstratified mica/montmorillonite, and montmorillonite (modified after Shimoda and Kohyama(1971), Shimoda (1974b), and Shimoda etaf. (1974)). 0Mica, illite. 0Montmorillonite. Beide lite. @ Allevardite, rectorite. @ Interstratified mica/montmorillonite, considered to be transformed from mica. X Interstratified mica/montmorillonite, considered to be transformed from montmorillonite. Same origin as 3,and found in the alteration area of Kuroko deposits. @ Origin unknown. Y: Yonago. G: Goto. F: Funyu. N: Niida. K1: Kamisunagawa-K1. K2: Kamisunagawa-K2.

8.3.2. Intevstrati$ed chlorite/montmorillonite

The mineralogical properties of interstratified chlorite/montmorillonites have been investigated by many workers, but few studies on their origin have been made in Japan. Nishiyama and Oinuma (1973) found a randomly interstratified chlorite/vermiculite in red shale of the Triassic system at Toyoma, Miyagi Prefecture. Based on its mode of occurrence, they concluded that the mineral was transformed from chlorite by leaching of its brucite layer during weathering. Ross and Kodama (1974) converted a preheated chlorite to a vermiculite-like material by treatment with HC1, and after adding NaCl solution. Subsequently, they succeeded in transforming chlorite to an interstratification (Ross and Kodama, 1976). In the Oshima-Fukushima district, Yoshimura (1971) demonstrated the formation of the interstratified minerals from montmorillonite by an aggrading process. In the so-called Green Tuff regions, the mode of occurrence and zonation of the alteration products usually indicate transformation of mont-

ORIGIN OF INTERSTRATIFIED MINERALS

317

morillonite to the interstratified minerals (Kimbara et al., 1971; Kimbara, 1973, 1975b) Wyart and Sabatier (1967) synthesized corrensite from montmorillonite by adding magnesium carbonate under hydrothermal conditions. Roy and Romo (1957) also demonstrated the transformation of vermiculte to an interstratification under hydrothermal conditions. These data appear to indicate the origin of the interstratified minerals found in the Kuroko deposits, although synthetic studies have not yet been done in Japan. Although interstratified dioctahedral chlorite/montmorillonite usually oc-

2"

7'

lo'

ze

(CUW

15'

Fig. 8.18. Pressure-temperatureequilibrium curves separating interstratified mica/montmoriIlonite, interstratified dioctahedral chlorite/montmorillonite, and mica (upper graph), and X-ray diffraction patterns for each phase (lower graph) (Matsuda and Henmi, 1973) A: Unchanged, starting material (interstratified mica/montmorillonite, and kaolinite), 1 and 2. B: Interstratified dioctahedral chlorite/montmorillonite, 3 and 4. C: Mica, 5. 1 : Starting material. 2: Treated at 200°C, 1 kb. 3: Treated at 380°C, 2 kb. 4: Treated at 390°C, 2 kb. 5: Treated at 59OoC, 1 kb.

318

INTERSTRATIFIED MINERALS

curs with interstratified micafmontmorillonite and kaolin minerals (Kanaoka, 1968, 1974, 1975; Shimoda, 1969; Nishiyama et al., 1975; Ichikawa and Shimoda, 1976), the relation between the two interstratified minerals has never been discussed. However, Matsuda and Henmi (1973) have synthesized an interstratified dioctahedral chlorite/montmorillonite from a mixture of a randomly interstratified mica/montmorillonite and kaolimite under 0.5-2 kb water pressure at 360480°C. The material obtained changes to mica above 480°C. The relationships between the minerals are illustrated in Fig. 8.18. This experiment provides useful information on the origin of the minerals and explains the altered liparitic rocks called Toseki, since most Toseki are composed of the two interstratified minerals, mica, and kaolin minerals (Kanaoka, 1968; Ichikawa and Shimoda, 1976). The Kakitani Toseki is an alteration product of pitchstone (intrusive rock as a dyke) (Tsukawaki, 1962). The altered pitchstone may be divided into 5 parts based on the suecessive mineral assemblages. These are, from the outer to the inner part of the pitchstone: (1) pitchstone-unaltered part of the parent rock, (2) a montmorillonite with small amounts of cristobalite and mordenite part, (3) an interstratified mica/montmorillonite with kaolinite and quartz part, (4) an interstratified dioctahedral chlorite/montmorillonite and quartz part, and (5) a mica and quartz part. The part rich in interstratified dioctahedral chlorite/montmorillonite provides a good Toseki for chinaware. Ichikawa and Shimoda (1976) studied the Hokuno Toseki and showed that the Toseki there is composed of interstratified dioctahedral chlorite/montmorillonite, interstratified mica/montmorillonite, kaolinite and quartz, The mineral assemblage thus corresponds to parts (3) and (4) of the Kakitani Toseki. They also converted a specimen composed mainly of interstratified mica/montmorillonite but with some kaolinite, to interstratified dioctahedral chlorite/montmorillonite under hydrothermal conditions at 450°C and 400 atm. This appears to indicate one process of formation of interstratified dioctahedral chlorite/ montmorillonite. REFERENCES Akai, J. (1974) J. Miner. SOC.Japan 11, 87. Akai, J. (1975) Earth Sci., 29, 153. Alexander, L. T., Hendricks, S. B. and Nelson, R. A. (1939) Soil Sci.48, 273. Alietti, A. (1956) Rend. Accud. Nuzl. Lincei. VIII-21, 201. Altschuler, 2. S., Dwornilk, E. J. and Kramer, H. (1963) Science 141, 148. Bradley, W. F. (1950) Amer. Miner.35, 590. Brindley, G. W. (1955) Amer. Miner. 40, 239. Brindley, G. W. (1956) Amer. Miner. 41, 91. Brindley, G. W. and Sandalaki, Z. (1963) Amer. Miner. 48, 169. Brown, G., and Greene-Kelly, R. (1954) Actu Cryst. 7 , 101. Brown, G. Brourguignon, P. and Thorenz, J. (1974) Clay Miner. 10, 135. Burst, J. 8. Jr. (1955) Chys Cluy Miner. Proc. 6th Nat. Conf., 327.

REFERENCES

319

Cole, W. F. (1966) Clay Miner. 6,261. Cole.,W . F. and Hosking, J. S. (1957) Clay Mineral Mixtures and Interstratified Minerals, in The Differential Thermal Investigation of Clays (ed. R. C. Mackenzie), Miner. SOC.London. Cole, W. F. and Neilson, M. E. (1958/1959) Mining Geol. J. 6, 35. Cradwick, P. D. and Wilson, M. J. (1972) Clay Miner. 9, 395. Dyakonov, Yu. S. (1961) Kristallographia 6, 624. Eroschev-Shak, V. A. (1970) Sedimentology 15, 115. Faust, G. T. and Murata, K. J. (1953) Amer. Miner. 38,973. Faust, G. T., Hathaway, J. C. and Millot, G. (1959) Amer. Miner. 44, 342. Gruner, J. W. (1934) Amer. Miner. 19, 557. Hayashi, H. (1961) J. Miner. SOC.Japan 5, 101. Hayashi, H., Inaba, A. and Sudo, T. (1961) Clay Sci. 1, 12. Hayashi, H. and Oinuma, K. (1964) Clay Sci.2, 22. Hayashi, M. (1972) Geothermics 9, 40. Hayashi, M. and Yamazaki, T. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 48. Hendricks, S. B., Nelson, R. A. and Alexander, L. T. (1940) J. Amer. Chem. SOC.62,1457. Hendricks, S. B. and Teller, E. (1942) J. Chem. Phys. 10, 147. Higashi, S. (1974) Clay Sci.4, 243. Higashi, S. and Shirozu, H. (1975) J. Clay Sci. SOC.Japan 15,78. Honeyborne, D. B. (1951) Clay Miner. Bull. 1, 150. Ichikawa, A. and Shimoda, S. (1976) Clays Clay Miner. 24, 142. Jiyama, J. T. and Roy, R. (1963) Clays Clay Miner. 10th Natl. Conf., 4. Ishikawa, Y.and Shimoda, S. (1974) J. Clay Sci. SOC.Japan 14,71. Ishizaka, T. (1969) Alteration at the Shakanai Mine, Spec. Pap., Shakanai Mine Co. Ltd. Kakinoki, J. and Komura, Y. (1952) J. Phys. SOC.Japan 7, 30. Kakinoki, J. and Komura, Y.(1954) J. Phys. Soc. Japan 9, 169. Kakinoki, J. and Komura, Y. (1962) Acta Cryst. 15, 292. Kanaoka, S. (1968) J. Ceram. Assoc. Japan 76, 72. Kanaoka, S. (1974) Mineralogical Studies on Toseki (China Stone, Pottery Stone), Ph. D. Thesis, Tokyo Kyoiku Daigaku. Kanaoka, S. (1975) Contributionsto Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 34. Kanno, I., Honjo, Y. and Arimura, S. (1960) Advances in Clay Science, voI. 2, p. 217, Gihodo. Kato, E. (1976) Znfvared Studies on Kaolin Minerals, Ph. D. Thesis, Tokyo Kyoiku Daigaku. Kato, Y. (1965) Soil Sci. Plant Nutr. (Tokyo) 11, 114. Katsumoto, N. and Shirozu, H. (1973) Sci. Rept. Dept. Geol. Kyushu Univ. 11, 231. Kimbara, K. (1973) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 68, 311. Kimbara, K. (1975a) Contributionsto Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 42. Kimbara, K. (1975b) Bull. Geol. Surv. Japan 26, 31. Kimbara, K. and Honda, S. (1975) Bull. Geol. Surv. Japan 26, 37. Kimbara, K. and Nagata, H. (1974) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 69, 239. Kimbara, K. and Shimoda, S. (1972) J. Clay Sci. SOC.Japan 12, 133. Kimbara, K., Shimoda, S. and Sato, 0. (1971) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 66, 99. Kimbara, K. and Sudo, T. (1973) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 68, 246. Kimbara, K. and Sumi, K. (1975) Geothermics 12, 59. Kimbara, K., Yoshimura, T., and Wakabayashi, S. (1971) Monogr. Assoc. Geol. Collab. Japan No. 17, 55. Kizaki, Y. (1970) J. Clay Sci. SOC.Japan 10, 52. Kobayashi, K. and Oinuma, K. (1960) J. Geol. SOC.Japan 66, 506. Kohyama, N. (1972) Mineralogical Study on Clay Minerals Found in the Tuffof Oya, Tochigi Prefecture, Japan, Ph. D. Thesis, Tokyo Kyoiku Daigaku. Kohyama, N. and Shimoda, S. (1974) J. Miner. SOC.Japan 11, 99. MacEwan, D. M. C. (1956) Kolloidzschrift. 149, 96. MacEwan, D. M. C. (1958) Kolloidzschrift. 156, 61. MacEwan, D. M. C. and Ruiz Amil, A., (1959) Kolloidzschrift. 162, 93.

320

INTERSTRATIFIED MINERALS

Martin Vivaldi, J. L. and MacEwan, D. M. C. (1957) Clay Miner. Bull. 4, 173. Martin Vivaldi, J. L. and MacEwan, D. M. C. (1960) Kolloidzschrift. 4, 173. Matsuda, T. and Henrni, K. (1973) J. Miner. Soc. Japan 11, 152. Mering, J. (1949) Actu Cryst. 2, 371. Mitsuda, J. (1957) Miner. J. 2, 169. Nagelschmidt, G. (1944) Miner. Mug. 27, 59. Negishi, T. (1967) J. Geol. Soc. Japan 73,407. Nishiyama, T. (1975) Contributions to Cluy Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 64. Nishiyama, T. and Oinurna, K. (1973) J. Cluy Sci. SOC.Japan 13,8. Nishiyama, T., Oinuma, K. and Ueda, F. (1973) J. Toyo Univ. Gener. Educ., Nut. Sci. 16, 21. Nishiyama, T., Oinuma, K. and Sato, M. (1974) J. Miner. Soc. Jupun 11, 142. Nishiyama, T., and Shimoda, S. (1974) J. Toyo Univ. Gen. Educ., Nut. Sci. 17, 1. Nishiyama, T., Shimoda, S., Shimosaka, K. and Kanaoka, S. (1975) Cluys Cluy Miner. 23, 337. Oinuma, K. and Hayashi, H. (1965) Amer. Miner. 50, 1213. Oinuma, K. and Hayashi, H. (1968) J. Toyo Univ. Gen. Educ., Nut. Sci. 15, 1. Oinuma, K. and Kobayashi, K. (1961) J. Geol. SOC.Jupun 67, 14. Osada, M. and Sudo, T. (1961) CZuy Sci. 1,29. Otagaki, S. (1968) Symposium, Alteration in the Green Tuff Region, 109. Otagaki, S., Tsukada, Y., Osada, T. and Fujioka, H. (1969) Mining Geol, 19, 285. Otsu, H. and Yasuda, T. (1964) Miner. J. 4, 91. Otsu, H., Shimazaki, Y. and Ohrnachi, H. (1963) Bull. Geol. Surv. Japan 14, 591. Powers, M. C. (1959) Cluys Cluy Miner. Proc. 6th Natl. Conf., 309. Price, N. B. and Duff, P. McL. D. (1969) Sedimentology 13, 45. Reynolds, R. C. (1967) Amer. Miner. 52, 661. Reynolds, R. C. (1970) Cluys Cluy Miner. 18, 25. Ross, G. J. and Kodama, H. (1974) Clays Cluy Miner. 22, 205. Roy, R. and Romo, L. A. (1957) J. Geol. 65, 603. Sato, M. (1965) Nature 208, 70. Sato, M. (1969) Z. Krist. 129, 388. Sato, M. (1970) J. Cluy Sci.Soc. Jupun 10,89. Sato, M. (1971) J. Miner. SOC.Japan 10, 36. Sato, M. (1973) J . Cluy Sci. Soc. Japan 13, 39. Sato, M. and Kizaki, Y. (1972) Z. Krist. 135, 219. Sato, M., Oinuma, K. and Kobayashi, K. (1965) Nature 208, 179. Sato, M., Tsuzuki, Y. and Yoshida, T. (1974) J . Miner. SOC.Jupan 11, 111. Sato, M., Goto, Y.,Kizaki, Y. and Matsuda, S. (1975) Contributionsto Clay Minerulogy,Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 54. Schultz, L. G. (1963) Chys Clay Miner. Proc. 11th Natl. Conf., 169. Schultz, L. G., Shepard, A. O., Blackmon, D. D. and Starkey, H. C. (1971) Cluys CZay Miner. 19,137. Shimoda, S . (1960) Advances in Clay Science, vol. 2, p. 115, Gihodo. Shimoda, S. (1969) Clays Clay Miner. 17, 179. Shimoda, S. (1970) Clay Miner. 8, 352. Shimoda, S. (1971) J. Clay Sci. Soc. Japan 11, 85. Shirnoda, S. (1971) C h y Miner. 9, 185. Shimoda, S. (1972) Clay Sci. 4, 115. Shirnoda, S. (1974a) J. Clay Sci. SOC.Japan 14, 79. Shirnoda, S. (1974b) Symp. Miner. SOC.Japan, Occurrence and Mineralogical Properties of Layer Silicate Minerals (ed. K. Henrni), p. 24. Shirnoda, S. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Reitrement, 92. Shirnoda, S. and Brydon, J. E. (1971) Clays C h y Miner. 19, 61. Shimoda, S. and Kohyama, N. (1971) J. Miner. Soc. Jupan 10, 162. Shirnoda, S. and Nishiyarna, T. (1973) J. Clay Sci. Soc. Japan 13,48. Shimoda, S . and Sudo, T. (1960) Amer. Miner. 45, 1069. Shimoda, S., Kohyarna, N. and Ishikawa, Y. (1974) J. Miner. Soc. Japan 11, 169. Shimoda, S., Oinuma, K. and Sudo, T. (1969a) Proc. Intern. Clay Conf. Tokyo 1969,1,197.

REFERENCES

321

Shimoda, S., Oinuma, K. and Negishi, T. (1969b) J. Geol. Soc Japan 75,591. Shimosaka, K . and Sudo, T. (1961) Clay Sci. 1, 19. Shimoyama, A., Johns, W. D. and Sudo, T. (1969) Proc. Intern. Clay Conf. Tokyo 1969,1,225. Shirozu,H. (1969) “Discussion” in Kodama et al., Hydrous Mica Complexes, Proc. Intern. Clay Conf. 1969 Tokyo, 2,64. Shirozu, H. (1974) Geology of Kuroko Deposits, Min. Geol. Spec. Issue, 303. Shirozu, H. and Higashi, S. (1972) Clay Sci. 4, 137. Shirozu, H. and Higashi, S. (1974) J. Miner. SOC.Japan 11, 180. Shirozu, H. and Higashi, H. (1976) J. Miner. SOC.Japan, in press. Shirozu, H., Date, T. and Higashi, S. (1972) Mining Geol. 22, 393. Shirozu, H., Ozaki, M. and Higashi, S. (1971) Clay Sci., 4,45. Shirozu, H., Sakasegawa,T., Katsumoto, N. and Ozaki, M. (1975) Clay Sci. 4,305 Shutov, V, D., Drits, V. A. and Sakarov, B. A. (1969) Proc. Intern. Clay Conf. Tokyo 1969,1,523. Spears, D. A. (1970) J. Sed. Petrol. 40, 386. Stephen, I. and MacEwan, D. M. C. (1951) Clay Miner. Bull. 1,157. Stoffler,D. (1963) Beitr. Z. Miner. Petrogr. 9, 285. Sudo, T. (1954) Clay Miner. Bull. 2, 193. Sudo, T. (1956) Sci. Rept. Tokyo Kyoiku Daigaku5, Sec. C, No. 43,39. Sudo, T. (1959a) Advances in Clay Science, vol. 1, p . 33, Gihodo. Sudo, T. (1959b) Mineralogical Study on Clays of Japan, Maruzen. Sudo, T. (1963) Proc. Intern. Clay Conf. Stockholm, 1963, 1, 113. Sudo, T. (1968) Symposium, Alteration in the Green Tuff Region, 171. Sudo, T. and Hayashi, H. (1955) Sci. Rept. Tokyo Kyoiku Daigaku 3, Sec. C, No. 25,281. Sudo, T. and Hayashi, H. (1956a) Nature, 178. 1115. Sudo, T. and Hayashi, H. (1956b) Clays Clay Miner 4th Natl. Conf., 389. Sudo, T. and Hayashi, H. (1957) Miner. J. 2, 187. Sudo, T., Hayashi, H., Kodama, H. and Shimoda, S. (1961) Mining Geol. 11, 356. Sudo, T., Hayashi, H. and Shimoda, S. (1962) Clays Clay Miner. 8, 373. Sudo, T., Hayashi, H. and Yokokura, H. (1958) Clay Miner. Bull. 3, 258. Sudo, T. and Kodama, H. (1957) Z. Krist. 190,379. Sudo, T. and Shimoda, S. (1969) The Clays of Japan, Gelrv. Suo. Japan 155. Sudo, T., Takahashi, H. and Matsui, H. (1954a) Nature 173,261. Sudo, T., Takahashi, H. and Matsui, H. (1954b) Japan. J. Geol. Geograph. 24, 71. Sugiura, S. (1962) J. Miner. SOC. Japan 5,311. Sumi, K. (1968) Geol. Surv. Japan Rept. No. 225, 1. Takahashi, K. (1959) J. Miner. SOC.Japan. 4, 151. Takeshi, H. (1958) J. Miner. SOC.Japan, 3, 388. Takeshi, H., Fujii, N. and Fujinuki, T. (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1, 369. Takeshi, H. and Uno, Y.(1971) Miner. SOC.Japan Spec. Pap. 1,98 (Proc. IMA-IAGOD Mtg. 1970, 1MA-Vol.). Takeshi, H. and Uno, Y.(1974) J. Miner. SOC.Japan 11, 162. Tettenhorst, R. and Johns, W. D. (1966) Clays Clay Miner. 13th Natl. Clay Conf., 85. Tomita, K. and Dozono, M. (1973) Clays Clay Miner. 21, 185. Tomita, K. and Dozono, M. (1974) J. Japan. Assoc. Miner. Pet. Econ. Geol. 69, 147. Tomita, K., Ito, H. and Oba, N. (1975) Contributions to Clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 59. Tomita, K. and Sudo, T. (1968a) Nature 217, 1043. Tomita, K. and Sudo, T. (1968b) Rept. Fac. Sci. Kagoshima Univ. 1, 89. Tomita, K. and Sudo, T. (1971) Clays Clay Miner. 19,263. Tomita, K., Yamashita, H. and Oba, N. (1969) J. Japan. Assoc. Miner. Petrol. Econ. Geol. 61, 25. Tsukahara, N. (1964) Clay Sci. 2, 56. Tsukawaki, Y.(1962) J . Ceram. Assoc. Japan 60, 68. Tsuzuki, Y. and Sato, M. (1974) J. Miner. SOC.Japan 11, 106. Ueda, S. and Sudo, T. (1966) Nature 211, 1393. Veniale, F. and Marel, H. W. van der (1968) Contr. Miner. Petrol. 17, 237. Veniale, F. and Marel, H. W. van der (1969) Proc. Intern. Clay Conf. Tokyo 1969, 1,233. Weaver, C. E. (1953) Bull. Geol. SOC.Amer. 64,921.

322

INTERSTRATIFIED MINERALS

Weaver, C. E. (1959) Clays Ciray Miner. Proc, 6th Natl. Conf., 154. Weaver, C. E. and Bates, T. F. (1952) Clay Miner. Bull. 1, 258. Wiewiora; A. (1971) Clays Clay Miner. 19,415. Wiewiora, A. (1972) Proc. Intern. Clay Conf. Madrid 1972, 1, 101. Wyart, J. and Sabatier, G. (1967) Bull. Groipe Franc. des Argiles XVIII, 33. Yora, M., Wakita, K. and Honda, S. (1973) Geothermics 10, 27. Yoshida, T. (1976) J. Miner. SOC.Japan 12, 354. Yoshimura, T. (1961) J. Geol. SOC.Japan 67, 578. Yoshimura, T. (1964) J . Miner. SOC.Japm 7, 45. Yoshimura, Y. (1971) Sci. Rept. Niigata Univ. Ser. E., Geol. Miner. 2, 1. Yoshimura, T. and Kimbara, K. (1974) J. Miner. SOC.Japan 11, 135. Yoshirnura, T., Kimbara, K., Tanaka, S., Ito, N. and Wakabayashi, S. (1975) Contributions to clay Mineralogy, Dedicated to Prof. Toshio Sudo on the Occasion of His Retirement, 115.

Index

Acid clay, 1 catalytic ability, 17 consituent minerals, 230 -, DTA, 230,234 -, genesis, 221 -, IR, 234 -, properties, 2 -, X-ray data, 230, 234 -, chemical composition, 234 Acid clay deposit, 224-27 Aliettite, 90, 97, 305 Allophane, 3,7,28,79, 105, 147, 149 -A, 106 B, 106 Allophane, acid strength, 171 -, allophane-like constituent, 149, 155 -, anion sorption, 175 -, CEC and AEC, 167 -, chemical composition, 147, 148 -, coordination status of aluminum, 174 -, density and porosity, 179 -, DTA and TG, 160 -, electron micrograph, 152 -, electrophoresis and dispersion, flocculation, 171 -, fibrous, 153 -, IR, 163 -, morphology, 119, 156 -, occurrence, 156 -, optical properties, 151 -, spherule, 157 -, spherical structure unit, 173 -, structural model, 181 -, surface acidity, 170 -, surface area, 178 -, tranformation to haloysite, 118 -, X-ray and electron diffraction, 157 Altered wall rocks of Kuroko deposits, see Chlorite minerals Alushtite, 90 Alumina-rich gel-like material, 149; see Allophane Aluminum, allophane, 174,181 -, imogolite, 174

-, chlorite and montmorillonite, 286 Aluminum-interlayer vermiculite, 51 , tricotahedral, 51 Ando soils, 105 Aquacreptite, 73, -, structure model, 79

-, -,

_--_

Bentonite, 2, 17

-, constituent minerals, 227 -, DTA and chemical composition, 228

-,

genesis 221

-, Na-, 222 -, hydrothermal origin, 222, 224 -, volcanic ash by chemical alteration, 222

-

Brittle mica minerals, 62 CEC, see Cation-exchange capacities Celadonite, 59, 60 -, chemical composition, 58 -, Oya-ishi, 60 Chair-like structure, hybrid of, see Aquacreptite, structure model Chlorite -, chemical composition, in schists, 244 -, chemical composition, with serpentine, 246, 253 -, chemical data, 247 -, Fe-, FeMg-, Mg-, 243 -, metallic ore deposits, 247 -, poly type, 244, 247, 250, 254 -, trioctahedral, 243 Chlorite minerals, 62, 139, 243 -, altered wall rocks of Kuroko deposits, 253 -, mode of occurrence of Kuroko deposits, 254 Classification -, chlorite, 243 -, clay minerals, 33 -, noncrystalline slay minerals, 148 Clay minerals (14A), in volcanic ash soils, 110 Clay-organic complex, 15 Constituent minerals, acid clay, 230 -, bentonites, 227 Cookeite, 92, 95

323

324

INDEX

-, abnormal, 314 Jmogolite, 3, 79, 108, 109, 147, 149, 153 Demixing hypothesis, 91 -A and B, 153 Deweylite, 72 Imogolite, CEC and AEC, 167 Diagenetic alteration, tuffaceous sediment. -, chemical compcktion, 147, 148 -, Yamanaka district, 251, 268 -, coordination status of aluminum, 174 Dickite, 190 -, density and poronity, 180 -, chemical analysis, 193 -, DTA and TG, 162 -, I R spectra, 193 -, electron diffraction, 159 -, occurrence, 189 -, electrophoresis and dispersion, floccu-, X-ray diagram, 193 lation, 171 Dioctahedral chlorite, see Sudoite -, IR, 163, 164 Distinction between kaolinite and hallysite, 210 -, morphology and occurrence, 156 Donbassite, 94 -, structural model, 182 -, surface acidity, 170 Electric polar hypothesis, 90 -, X-ray diffraction, 158 Intercalation, kaolinite-potassium acetate Ferroan nontronite, 47 complex, 16 Intermediate clay mineral concept, 90, 92 Gaerome clay, 200 Interstratification Garnierite, 66, 68 -, alteration area, 269, 270 Geothermal alteration, 28, 191, 273 -, chemical composition, 294 Gibbsite, 113 -, DTA, 292 Green tuff, 20, 251 -, electron microscopy data, 298 -, Tanzawa Mountains, 21 -, green tuff or amygdales, 268 -, region (in map), 128 -, IR, 294 -, lattice image, 299 -, synthesis, see Synthesis of InterstratifiHalloysite cation -, chemical data, 201 -, X-ray data, 288 -, chestnut shell-like particles, 80, 81, 85 Interstratified chlorite-montmorillonite, 24-6, -, electron diffraction patterns, 205 93, 95, 286, 314 -, hydrothermal, 196 Interstratified chlorite-saponite -, IR data, 206 -, chemical composition, 257 -, lattice image, 84 -, X-ray data, 254 -, morphology, 119, 208 Interstratified chlorite-vermiculite, 253 -, spherules, 80, 122, 157, 196, 208 Interstratified dioctahedral chlorite-montrnoril-, stability of interlayer water and in 6-dimenlonite, 270, 272, 273 sions, 205 Interstratified FeMg chlorite-saponite, 251 Heavy clay, 7, 19 Interstratified Mg chlorite-saponite, 141, 253 Niru-ishi, 51 Interstratified kaolin-montmorillonite, 90, 299 Hisingerites, 85, 89, 151 -, acid clay, 274 -, Oya, 87 -, chemical composition, 305 Hollow spherules, 182 -, DTA, 304 Hydromuscovite, 52; see u h Sericite -, IR, 307 Hydrothermal alteration, 24, 26, 196, 269, 270 -, X-ray data, 299 -, Toseki, 194 Interstratified mica-chlorite, 307 -, wall rock alteration of Kuroko deposits, -, chemical composition, 309 24, 26, 130-34 -, DTA, 308 -, zonal distributiol~,271, 273, 318 -, occurence, 267 -, X-ray data, 307 Illite, 51, 52 Interstratified mica-montrnorillonite, 266 Corrensite, 90, 97

INDEX

-,

alteration area of Kuroko deposit, 270 chemical composition, 282 DTA. 276 -, diaspore-pyrophyllite deposits, 272 -, electron microscopy data, 286 -, geothermal areas, 273 -, lattice image, 286 -, mode of occurrence, 266,314 -, origin, 312 -, X-ray data, 215 Interstratified minerals, 5, 89, 265 -, calculation of diffraction pattern, 4 -, mode of occurrence, 266 lntesrtratified mica-sudiote, 134, 142 Interstratified trioctahedral chlorite-saponite, 293 Interstratifid trioctahedral chlorite-vermiculite, 294 Iron-rich montmorillonite, 21, 47; see also Ironsaponite -, iron-bearing montmorillonite beidellite, 43, 45 Iron sand bed, 38 Iron-saponite, 38, 40, 43, 45, 233 -, analog, 47 -, chemical composition, 233 -, DTA, 234

-,

-.

Kanto volcanic ash beds, see Loam, Kanto Kaolin, 63, 113, 142, 189 -, alteration of pumice or tuff, 200 -, genesis, 207 -, high temperature phase, 14 -, Hong Kong, 5 -, hydrothermal, 193, 211 -, sedimentary, 200, 201 Kaolinite, 16 -, chemical data, 201 -, 1R data, 205 -, morphology, 206 -, occurrence, hydrothermal, 193 -, occurrence, weathering and sedimen’ary, 198 -, X-ray data, 203 Kaolinitic fireclays, 200 Kibushi clay, 200 Kuroko, 23, 127 -,alteration, 130, 131 -, genesis, 129 -, gypsum deposit, 129, 136 -, mineralization, 12 -, origin, 268

325 -, stock-work deposit, 129, 135

-, vertical zoning of constituents, 129 Lattice image, 5, 15

-, hallysite, 84

-,

interstratified chlorite-montmorillonite, 299 -, interstratified chlorite-montomorillonite, 299 -, interstratified mica-montmorillonite, 286 Loam -, Daisen, 8 -, Kanto, 81, 114 -, Musashino, 114, 115 -, Shimosueyoshi, 90, 114, 115 -, Tachikawa, 114, 115 -, Tama, 114, 115 Marine sediment, 12

-, Recent, 29, 47 Montmorillonite, 37, 142, 221

-, abnormal, 230, 310 -, transformation to halloysite, 230 -, weathering, 233 Magnesian chlorite minerals, 253; see also chlorite minerals Montnorillonite-halloysite, mixed-layers, 222, 232, 236 Morphology, allophane, 119, 156 -, hallysite 119, 209 -, imogolite 156 -, kaolinite, 208 Morphological study of clay particles from pyroclastics, Kanto district, 122 Na-bentonite, see bentonite Nacrite, 191 -, chemical analysis, 193 -, JR spectra, 193 -, occurrence, 189 -, X-ray diagram, 193 Nontronite, 239 -, chemical composition, 240 -, DTA, 239 Opaline silica, 107 Oya-ishi (Oya-stone), 42 Palygorskite, 66 Penwithite (neotocite), 85 Pumice, Imaichi, 115, 118, 119

326

-, Kanuma, 115,119, 122 -, Kitakami, 123

-, Shichihonzakura, 115, 118, 119

-, Tokyo, 115

Pyroclastic deposit, Hokkaido, 115

-, Kanto district, 114, 122 -, Hachinohe, east of Yatsugatake volcano, Shiojiri and Ina, Ashitaka volcano and Daisen volcano, 117 Pyrophyllite, 35, 142 Rapid quantitative analysis, 10 Rectorite, 89 Roseki, 24, 189. 193 -,zonal sequences, 211 Sepiolite, 66

-, iron-, 66 Serpentine, 18, 63, 142 Sericite 17, 52, 53, 130, 132, 136 -, mineralogy, 136 Smectite, 37, 142, 221 Soil-lime engineering method, 19 Spherule, see Halloysite, spherules Spherulitic halloysite, 80 Stevensite, 240 -, chemical composition, 241, 310 -, DTA, 310 -, interstratified structure by dehydration, 309 -, IR data, 310 -, X-ray data, 310 Sudoite (dioctahedral chlorite = Al-rich

INDEX chlorite), 24, 92, 134, 141, 259

-, chemical composition, 261, 262

-, Kuroko deposits, 260 -, occurrence, 25 -, X-ray data, 260

Sudoite-montmorillonite,see Tosudite Swelling chlorite, 90, 251, 253 -, X-ray data, chemical composition, 255 Synthesis of interstratification, 13, 91, 315, 318 Talc, 35, 143 Toseki, 26, 194 -, composition, 272 -, hydrothermal alteration, 194 Tosudite, 24-6, 90, 93, 95, 134, 141, 259, 272 -, occurrence, 273 Trioctahedral chlorite-saponite, 288 Tuffaceous sediment, see Diagenetic alteration, Vermiculite

-, Mg-, Al-interlayer, 50 Volcanic ash, 2, 9, 106, 147 -, marine deposition, 115 -, mineralogy, 105 -, occurrence, 28 Weathering of montmorillonite, acid clay deposits, 233 Zeolite, 92, 130 Zonal distribution, 271, 273 -, clay mineral, 270