Investigations of micro-structure of clays by electron microscopy are reviewed, -(1) shape and crystal habits, (2) dispersion and aggregation of particles and transformation of crystals, (3) surface structure and epitaxy, (4) inner structure of crystals, (5) lattice images of crystals, and (6) crystal structure images.
Especially, the studies of clays have been done at the Institute for Chemical Research, Kyoto University are stated. Lattice images of a clay-organic compound and crystal structure images of mica-smectite are observed directly by a high resolution electron microscopy.

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In considering the historical information about the development of the studies on clays and clay minerals, it is known that there are several large trends of studies which started in olden times and have kept on developing till the present, and will promise to make further advance in future, having interesting fundamentals, high potentialities, and wide application. Attention may first be drawn to the development of the field of the studies on the chemical affinity of clay minerals. This article attempts to account the outline of the studies in this field. The contents, however, are slightly different from the traditional review the object is, rather, to see what light may be thrown on typical phenomena in this field by a general and inclusive concept.(1) In the first place, the writer gave a brief account of the special quality of the studies on “acid clay” performed by K. Kobayashi (the late Emeritus Professor of Waseda University) and his collaborators. The studies are regarded to be the foremost works in this field.(2) The role of the chemical affinity of clay minerals has been demonstrated in various chemical reactions between clay minerals and inorganic or organic materials. In the second place, therefore, the nature of clay-organic complexes or clay-organic derivatives was briefly explained with special reference to their structural implications.(3) The chemical and structural behaviours resulted from the chemical affinity of clay minerals have been studied in several aspects in terms of surface-chemical and topochemical reactions, epitaxy, and catalysis. In the third place, the writer gave a brief account of the studies on epitaxy observed among various kinds of materials, and stressed its significant in clay mineralogy.(4) In the fourth place, the writer stressed that it is significant and interesting to study the typical phenomena resulted from the chemical affinity of clay minerals from a point of view standing on the general and inclusive concept, that is, the template theory (“Matrizenprincips”) set fourth by H. Seifert.(5) In learning the current studies concerning the role of clays and clay minerals in the aspects such as the generation of petroleum, the origin of life, and the environmental science, particular attention was paid on the facts and concepts that clay mineral have acted as templates.

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Recent advances in the study of non-and para-crystalline clay minerals have brought about a better understanding of the chemical bonding and functions of active Aluminum not only in these minerals but in other components of Kuroboku soils. The former minerals are allophane and imogolite, and the latter components Al-humus complexes and allophanelike constituents. Their genesis-transformation, structural chemistry and functions in ion exchange and specific adsorption were discussed and correlated on the basis of avail-able data.

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Recently, it was found that the superconducting critical temperature of some transition metal dichalcogenides were strongly influenced by intercalating pyridine molecules. Since this discovery, the synthesis and characterization of intercalated inorganic compounds are attaining a position of consequence in the field of material science. The present paper is concerned with few characteristic examples of such intercalation compounds; i. e. stereospecific synthesis of coordination polymers in the interlayer space of layered inorganic compounds, effects of the intercalated organics on magnetic and electrical properties of host materials, grafting products of organic chains onto the interlamellar surfaces of layered inorganic compounds.

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Methods of isolation and analysis of the particulate materials in the human tissues are reviewed. Since the relation of asbestiform minerals to human disease has been well documented, individual asbestos fibres and/or body cores in lung tissues have been sub-ject of observation by transmission electron microscope. Recently analytical electron microscope has been developed to facilitate observations for morphological and structural and chemical characteristics on the same specimen with an instantaneous switching. A carbon extraction technique used in association with analytical electron microscope provided evidence for the presence in the human tissues of quartz, sericite, talc, pyrophyllite, kaolin, diatomaceous material and some types of asbestos fibres. Applying a method of quantitative analysis for thin specimens by energy dispersive X-ray spectrometer, more than a quarter of the whole MgO contents leached out from chrysotile fibrils by their residence of 28 months in the rat lung.
The biological and tissue responses on exposure of asbestos fibres are also reviewed from a molecular biological viewpoint.

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Recent progress in clay science, which has been mainly made in the mineralogical field, has contributed strikingly to the investigation for the ceramic raw material. The modern analytical methods have been successful in the standardization and the simple classfication of clay minerals, but many ceramic technological problems such as the complexity and diversity on both clay mineral property and clay mass structure have not been yet clarified. In this paper the Seger's classical treaties (‘The process of weathering of crystalline rocks and its influence of the structure of clay bodies’ and ‘Crystallization and its significance on the clay industries’, the collected writings of H. A. Seger (1903), 1-7 and 8-31) are reviewed, where he tried to understand the variety of clay by observing in detail the process of weathering of feldspathic rocks and of formation of clayey sedimentary rocks. Particularly he discussed the function of water in the change of materials and in the formation of hard sedimentary rocks in nature and also in the processing of ceramic clay materials.

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There are closed relationships between clay minerals and drilling muds. In this paper, the following items are described.(1) Classifications and characteristics of clay minerals used for drilling muds.(2) Influences and controlling methods of clay minerals for mud rheology.(3) Classifications and characteristics of troublesome shales for drilling.(4) Hydration mechanisms of shales.(5) Effects of inorganic salts and polymers for hydration and dispersion of troublesome shales.(6) Inhibited muds.(7) Others.

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Construction projects encounter often problems which are concerned with the characteristic of clay minerals. In one way, clays bring difficulties into construction, and in another, they can be utilized favorably.
The knowledge of clay science is necessary not only for survey, design, material, site work and maintenance of construction projects, but also for conservation of environment, prevention of disaster and disposal of waste products. As clay specialists are few in the construction field of Japan, co-operation and understanding of various clay scientists are needed in the field. As the problems of soil mechanics field, the present paper deals with the relation between soil characteristics and mineralogical structures of clays as well as the relation between soil stabilization and chemistry of clays. As the problems of concrete field, the paper handles harmful clays in aggregates, useful clays for pozzolanic action and for raw material of light weight aggregates as well as the structural similiarity between hydration products of cement and clay minerals. As the problems of disaster prevention, the paper refers to land slide, swelling and deformation of tunnel as well as settlement of ground. Further, the paper touches upon solidification of waste products and very soft alluvium soils, oxygen deficiency in underground work sites, and silicosis due to clay materials.

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