Electron-Diffraction Analysis of Clay Mineral Structures

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.

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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.

Contenu
1 Structures and Structure Modifications of Layer Silicates.- 1. General Introduction to the Structures of Layer and Pseudolayer Silicates.- 2. Some Features of the Structures of Individual Layers.- 3. Use of Structural Polyhedra in the Description and Analysis of Layer Silicate Structures.- 4. Polymorphic and Polytypal Modifications and Repeat Sequence Methods in Layer Silicates.- 5. Regular Structures of Two-Storied Kaolinite-Type Layers.- 6. Regular Structures of Three-Storied Mica-Type Layers.- 7. Regular Structures Made Up of Chlorite Packets.- 2 Experimental Electron-Diffraction Methods of Studying Minerals.- 1. Electron-Diffraction Apparatus.- 2. Preparation of Specimens for Study.- 3. Electron-Diffraction Patterns and Their Analysis.- 3 The Geometrical Theory of Electron Diffraction and Analysis of Clay Mineral Diffraction Patterns.- 1. Theoretical Basis of the Relationship Between the Crystal Lattice and the Diffraction Pattern: The Reciprocal Lattice.- 2. Geometrical Analysis of Electron-Diffraction Patterns.- 3. The Distribution of Reflections on Ellipses on Electron-Diffraction Texture Patterns from Layer Silicates.- 4 The Determination of Intensities in Layer Silicate Diffraction Patterns.- 1. General Comments.- 2. Analysis of Intensities in the Investigation of Layer Silicate Structures.- 3. Wave-Scattering by a Silicate Layer Sequence.- 4. The Distribution of Intensities in Layer Silicate Structure Modifications.- 5. Geometry of Layer Silicate Structural Features, as Revealed Through the Distribution of F or | F | 2.- 6. Effect of Variations in Chemical Composition on the Intensity Distribution in Layer Silicates.- 5 Experimental Electron-Diffraction Studies of Clays and Related Minerals.- 1. The Determination of Crystal Structures.- 2. Uncertainty in theNacrite Structure.- 3. Electron-Diffraction Data on Sepiolite and Palygorskite Structures.- 4. Investigations Using the Microdiffraction Method.- 5. Some Achievements of Electron-Diffraction Studies of Clays, Clay Minerals, and Related Layer Silicates by the Oblique Texture Method.- 6. Possible Fields of Application of the Electron-Diffraction Method in the Study of Minerals Which Are Not Layer Silicates.- Literature Cited.