Table Of Contentelectron-diffraction
analysis of
clay mineral structures
Monographs in Geoscience
General Editor: Rhodes W. Fairbridge
Department of Geology, Columbia University, New York City
B. B. Zvyagin
Electron-Diffraction Analysis of Clay Mineral Structures-1967
E. I. Parkhomenko
Electrical Properties of Rocks-1967
In preparation
A. I. Perel'man
The Geochemistry of Epigenesis
electron- diffraction
analysis of
clay :mineral structures
Revised Edition
Boris Borisovich Zvyagin
Institute for Geology of Ore Deposits, Petrography,
Mineralogy, and Geochemistry
Academy of Sciences of the USSR, Moscow
Translated from Russian by
Simon Lyse
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PLENUM PRESS· NEW YORK· 1967
TSBN-13: 978-1-4615-8614-2 e-TSBN-13: 978-1-4615-8612-8
DOT: 10.1007/978-1-4615-8612-8
Library of Congress Catalog Card Number 65-17783
The original Russian text, first published for the Institute
for Geology of Ore Deposits, Petrography, Mineralogy, and
Geochemistry of the Academy of Sciences of the USSR by
Nauka Press in Moscow in 1964, has been extensively cor
rected and updated by the author for the English edition.
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ELEKTRONOGRAFIYA I STRUKTURNAY A KRISTALLOGRAFIYA GLINISTYKH MINERALOV
ELECTRON-DIFFRACTION ANALYSIS OF CLAY MINERAL STRUCTURES
© 1967 Plenum Press
Softcover reprint of the hardcover 1st edition 1967
A Division of Plenum Publishing Corporation
227 West 17 Street, New York,N. Y.10011
All rights reserved
No part of this publication may be reproduced in any
form without written permission from the publisher
PREFACE TO THE AMERICAN EDITION
As a method of structure analysis, electron diffraction has its own spe
cial possibilities and advantages in comparison to the X -ray method for the
study of finely dispersed minerals with layer or pseudolayer structures. How
ever, possibly because of the prior existence of the X-ray method, which found
universal application in different fields and attracted the main efforts of spe
cialists, electron diffraction has been unevenly disseminated and developed in
different countries. In particular, the oblique texture method, which gives
very complete and detailed structural information, has been mainly used in
the Soviet Union, where electron-diffraction cameras specially suited to the
method have been constructed. In other countries, studies have been made of
micro-single crystals, because these studies could be carried out with existing
electron microscopes. It should be recognized that the scale of distribution
and use attained by electron-diffraction methods, at present limited by exist
ing experimental conditions. is more than justified by the value of the results
which may be obtained by their aid. The author hopes that the present book
will give the reader a fuller idea of the valuable advantages of the method,
and of the structural crystallography picture which has been built up for clay
minerals, and layer silicates in general, from electron-diffraction data.
The time between the appearance of this book and that of the Russian
edition has been comparatively short. During this period, however, new data
and results have been obtained in the fields of electron diffraction and struc
tural crystallography,. forming a significant addition to the original content of
the book. Unfortunately, Within the time at his disposal, the author has been
able to include only that new material produced by himself or his COlleagues.
The additional material has allowed certain gaps to be filled and some
confused topiCS to be clarified. It in.cludes an explanation of the structural di
versity and specific features of the serpentine-type minerals, a consideration
of the significance and role in structural crystallography of semi -random layer
silicate structures, a clarification of the position of halloysite as a special
member of the kaolinite group, a detailed examination of the features of dif-
v
vi PREFACE TO THE AMERICAN EDITION
fraction patterns from chrysotile tubes and their structural interpretation, a note
on the diagnostic features of semi -random varieties of micas of different
chemical composition and chlorites differing in the structures of their packets,
etc. It will be appreciated that there are many unresolved problems still re
maining. There is a great need to make use of the possibilities offered by
structure analysis in order to lead to further progress in our knowledge and
understanding of layer silicate structures.
PREFACE TO THE RUSSIAN EDITION
Clay minerals are used in many branches of science and technology and
figure significantly in the economy. Clays have found well-known uses as
catalysts and absorbents, fillers and pigments, and binding and cleansing agents.
They play an important part as raw materials in cement and ceramic produc
tion, they are the most significant factor in determining the fertility and sta
bility of soils, and they serve to indicate the formation conditions of sediment
ary rocks and the presence of certain types of minerals in prospecting (Grim,
1960).
The study of the crystal structures of clay minerals is of the highest
practical importance in every respect. Clays and clay minerals are deserving
subjects for structure analysis, which is necessary for them because of theirdi
versity and structural complexity.
Original and valuable information on the structures of clay minerals and
important practical results may be obtained by methods based on the diffrac
tion of electrons, which have special possibilities in this field. Electron-dif
fraction analysis of clay minerals forms a separate branch of electron-diffrac
tion methods, and occupies an independent position in the group of methods
used in the study of clays.
The application of electron diffraction to the investigation of clay min
erals developed under favorable circumstances in the Soviet Union.
It was assisted, above all, by the very high level of development ofelec
tron diffraction methods in this country. The books written by Z. G. Pinsker
(1949) and B. K. Vainshtein (1956) played an important part. laying the foun
dations of structure analysis by electron diffraction. Under their influence.the
unique image of Soviet electron-diffraction work was developed. character
ized in particular by the discovery and utilization of the rich store of informa
tion obtainable from electron-diffraction texture patterns through the applica
tion of Fourier analy~is methods. Electron-diffraction cameras of great prac
tical utility were devised and constructed in the USSR. Electron diffraction
vii
viii PREFACE TO THE RUSSIAN EDITION
became an essential tool in the study of the structures of materials. used for
the most diverse substances and applications. In its whole range of applica
tions. this remarkable physical phenomenon on one hand led to the discovery
of special laws of its own. and on the other provided objective results on the
properties of the objects scattering the electrons; it also allowed evaluation of
the stage reached by changes which might occur during the course of an in
vestigation.
In the study of clay minerals which. because of their special properties.
were natural candidates for application of the method. it was inevitable that
electron diffraction would mark the advent of a new. fruitful approach.
Clay minerals show great variability and diversity in their chemical
composition. geometry. and degree of structural perfection. and thus are byno
means always suitable for immediate use in detailed structural investigations.
In this connection another important factor in the development of electron
diffraction clay mineral analysis. leading to an increase in its effectiveness.
was the work of N. V. Belov on structural mineralogy and structural crystal
lography (1947. 1949. 1950. 1951a.b). This laid the foundations for the de
rivation of general laws for the formation and diffraction properties of struc
tures. with the guidance of which it was possible to evaluate the atomic struc
tures of clay minerals even with only a meager amount of diffraction data.
Thus. the intimate parmership of a structural analysis method with a
structural synthesis theory, electron diffraction with structural crystallography.
was dictated by the specific characteristics of clay minerals. It also made
possible a concrete, unrestricted approach to the treatment of diffraction pat
terns and to the analysis of their structural meaning. which also was of funda
mental importance in clay mineral work.
It should be noted that electron diffraction of clay minerals began its
development during the period when the basic concepts of silicate atomic
structures, in particular those of layer silicates, had already been worked out
byX -ray methods of structure analysis, where they resulted in the general
theories of Bragg (1937), Pauling (1930a,b), and Belov (1947. 1949). In more
recent times as well, the X-ray method has continued to be used in innumer
able and widely varying investigations, a large number of which have been
specially devoted to clay minerals (Brindley, 1955; Frank-Kamenetskii.1958;
Brown. 1961}; these have continued to build up valuable factual material,
which has apparently had a beneficial effect on the development of electron
diffraction mineral studies also.
PREFACE TO THE RUSSIAN EDITION ix
Together with X-ray structure analysis, electron diffraction occupies a
special position among investigational methods. These two methods reveal
the primary characteristics of a substance, which directly and unambiguously
determine all its properties, its special features, and its individuality. The
scope, function, and applications of the two methods in the study of minerals
may be compared as follows.
The X-ray method gives the general structural characteristics of the
rock being investigated. The X-ray photograph gives indications of all the
mineral components present in the specimen, over a wide range of particle
sizes. Electron diffraction, on the other hand, shows up only the finest frac
tion, so that electron-diffraction patterns principally reveal the minerals with
platy or needle-shaped particles.
There is no doubt as to the importance of obtaining a complete picture
of the mineral composition of a test material. At the same time, it shoUld be
remembered that the components forming the coarse fractions are usually
known from optical studies. In diffraction patterns these coarse particles usu
ally appear in the role of annoying obstacles to the straightforward determina
tion of the structural characteristics of the finely dispersed minerals. To re
solve many problems it is necessary to determine the structural characteristics
of the fine particles in question, which in most cases are clay minerals. In
addition, the possibility cannot be excluded that different size fractions of the
same mineral may differ somewhat in structure or ordering, and to clear this
up it is necessary to use both methods.
The advantage of the X-ray method is that the specimen may be in
vestigated in its natural state or over a whole range of conveniently chosen
states. The electron-diffraction method places the specimen under rigidly
circumscribed and, atthe same time, abnormal conditions-those ofa high va
cuum. In the majority of minerals the vacuum does not cause any structural
changes. Only specimens containing weakly bound water molecules are like
ly to suffer any effects. It is in fact found that the so-called swelling layer
silicates (montmorillonites and vermiculites) may be deprived of their inter
layer water, so that the whole of the dynamics of structure transformation with
change in moistness of the surrounding medium, and the characteristics of
mixed-layer products, become inaccessible to electron-diffraction investiga
tion. In all probability this limitation on the use of electron diffraction is not
absolutely exclusive. Thus, some vermiculite specimens, kindly presented by
G. f. Walker, and studied in detail by him previously (Mathieson, Walker,
1954), did not show loss of interlayer water molecules under electron-diffrac-
x PREFACE TO THE RUSSIAN EDITION
tion conditions. It may also be assumed that as experimental methods are
improved, this difficulty may also be obviated for other swelling minerals as
well
However, in spite of the foregoing, there is some positive value in the
fact that in electron diffraction the swelling minerals are studied in a strictly
fixed state which is itself also worthy of attention, particularly in connection
with the fact that in this state the structure is most highly ordered, thus allow
ing concealed features to be brought out. It should also be taken into account
that under vacuum conditions, electron diffraction may be used to investigate
structures which are unstable under natural conditions, as, for example, in the
study of the monohydrate BaCl2 • H20 (Vainshtein, Pinsker, 1949).
Another factor concomitant to electron-diffraction studies, i.e., bom
bardment with electrons, does not have any marked effect on the specimens
because the energy absorbed by them is comparatively small. If the electrons
interact more intensely with the substance (as, for example with microdiffrac
tion methods) the time of exposure of the specimen must be reduced, while
structural changes observed to occur may serve as an additional characteristic
of the crystalline substance.
With finely dispersed minerals, the electron-diffraction method will
give a special kind of diffraction pattern, the texture pattern, which contains
a two-dimensional distribution of a regularly arranged set of reflections; this
is found to be highly productive for the derivation of the structural features of
the specimen under study. However, these patterns, when obtained by the
transmission method from a platy texture, lack the OOl basal reflections from
the planes parallel to the silicate layers. It is true that these reflections can
be recorded on texture patterns obtained by the reflection method, but there
are considerable experimental difficulties with this at present.
In X-ray analysis of clay minerals the opposite situation prevails. The
general hkl reflections are arranged in a one-dimensional sequence in order
of decreasing value of their interplanar distances dhkl, and there are difficul
ties in indexing and measuring the intensities of these reflections. On the
other hand, the OOl basal reflections are easily recognized on ordinary X-ray
powder photographs and are mostly separated out with special types of photo
graphs in studies of oriented aggregates.
The OOl basal reflections express the features of the structure which are
contained in its projection along a direction perpendicular to the silicate
layers. This projection gives a great deal of information on the layer silicate
