In soils, we can find clay minerals, whose formation is more or less specific to soil environment. Their structures and properties as well as formation processes provide unique and interesting subjects in clay mineralogy. Examples are taken in this review based on the author's own interest. Studies on allophane, imogolite' and halloysite have shown that weathering of finely comminuted volcanic ash well reflects the effects of climate, vegetation, and time, and produces minerals of unique structures. “Vermi culite or smectite-chlorite intergrades” have been reported in many temperate soils, but there are indications that their “interlayer” materials are other than polymer hydroxy-aluminum ions. A possibility that at least some of these “intergrades” represent an intermediate phase in the transformation from a 2:1 type layer silicate to a 1:1 or another 2:1 type layer silicate during weathering is suggested.

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Mineralogical properties of sericite which was one of the main clay minerals in Amakusa pottery stones were studied by X-ray powder diffraction analysis, infrared absorption analysis, electron microscopic observation, etc., Some features of the pottery clay were also discussed according to the difference between two kinds of pottery stone veins. The results were summarized as follows;
(1) The half width of (001) of sericites included in Sarayama vein showslarger values than those in other veins of Amakusa pottery stone according to the statistical analysis of about 250 kinds of pottery stones. Sericites of Kaigan and Murayama veins are almost the same values in half width of (001).
(2) The clay minerals included in the pottery clay were separated into various particle size ranges by elutriation. The ratio (W₀₀₁/W₀₀₂) of (001) and (002) reflections of sericites (C-1, C-3) were plotted against particle size. The W₀₀₁/W₀₀₂ of C-1 is larger than 1.0 for the part under 0.5μm, and is larger than 1.0 for the one over 5μm. The W₀₀₁/W₀₀₂ of C-3 is larger than 1.0 for the part under 2μm. From these facts it is assumed that both sericites of C-1 and C-3 include less than 5% expandable layer.
(3) The properties of interlayer sites of sericites were analysed by infrared absorption spectra. Fine grained sericites (-0.5μm) in Sarayama and Kaigan veins have a small amount of water molecule and ammonium ion respectively. Electron micrographs of fine sericite particles (S-1) exhibit mostly long pillar shape and those of S-2 show mostly rectangular shape.
(4) Fine grained sericites show almost 1M polytype in Denbe-ekoba deposite, however, in Shimizuotoshi deposite they include a small amount of 2M₁ polytype. The coarse grained sericites (+20μm) from every pottery stone vein are the mixture of 1M and 2M₁ polytypes. Infrared absorption spectra also indicate that ammonium ions are included in coarse grained sericites.

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Two kinds of pottery clays (TS-1, TS-2) have been prep ared by pulverizing Amakusa pottery stone and two sorts of sericites (5-1, S-2) by elutriating the two pottery clays, respectively. Dispersion and coagulation properties of suspended pottery clays (TS-1, TS-2) and surface charge of sericites (5-1, S-2) have been studied as a function of pH on the basis of the data for zeta potential and the DLVO theory.
Two kinds of sericites showed almost the same value of zeta potential in high pH region, however, the values of 5-1 were smaller than those of S-2 at pH below 7. Surface potential, Stern layer and Guoy layer charges of S-1 and S-2 were calculated on the assumption that the edge potential was + 2 mV at pH 7. The surface potentials of S-1 and S-2 were-74 mV and-60 mV, respectively.
In the coagulation series tests, sediments in coagulated suspensions of TS-1 were more voluminous than those of TS-2 of the same solid concentration under the conditions of pH below 7 or above 12. The difference between the structures of both sediments in coagulated suspensions was analyzed by the DLVO theory including the particle size effects. It was difficult to consider that three types of association (face-to-face, face-toedge, edge-to-edge) occurred simultaneously or to the same extent, when a suspention of very thin plate-like clay minerals coagulated in water. At the early stage of coagulation, edge-to-edge association was considered to play an important role in determining the structure of sediments because a potential energy barrier of edge-to-edge association in case of the very thin particles became much lower than the average kinetic energy of particles (15kt). It was therefore concluded that thin particles exhibited voluminous coagulation than thicker particles.

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Beryllosilicate (BeZSM-5) and aluminoberyllosilicate (AlBeZSM-5) with ZSM-5 structure were synthesized at 100°C from clear solutions in the system Na₂O-TPA₂O-BeO-SiO₂-H₂O. Crystals of these compounds grew up to 8μm in period of 21 to 28 days. The AlBeZSM-5 contained a small amounts of alumina which came from alumina impurity present in a silica source. The BeZSM-5 contains Be atoms in the range of 1.50 to 12.74 and Al atoms in the range of 0.03 to 0.06 per unit cell, whereas the AlBeZSM-5 contains Be atoms in the range of 0.58 to 4.59 and Al atoms in the range of 0.65 to 1.20 per unit cell. The isomorphous replacement of Si by Be did not lead the change in lattice constants, and hence it is considered that interatomic distance Be-O in these compounds is approximately equal to Si-O distance.
The relation between the catalytic activity for methanol to hydrocarbons conversion reaction over HBeZSM-5 and HAlBeZSM-5 catalysts and the Be contents in these catalysts were examined. The catalytic activities of HBeZSM-5 increased with increasing Be content, although they were lower than those of HZSM-5. The major products over the HBeZSM-5 were aliphatic hydrocarbons including C₂ and C₄ ones. This may be due to the fact that Be atom brings about an increase in the number of acid sites in this catalytic system. The HAlBeZSM-5 showed high activity ranging from 95 to 100% in the conversion of methanol to hydrocarbons. These results indicate that Al atoms in the framework of this catalyst enhance its catalytic activity and the acid strength of H-AlO₄ tetrahedron is stronger than that of H-BeO₄ one.
The ratios of aliphatic hydrocarbons to aromatic ones formed over HAlBeZSM-5 catalysts are high compared to those over HZSM-5 catalysts. The main aliphatics formed are n-and iso-C₄, but their product distributions shift to the side of lower molecular weight hydrocarbons with reaction time as the Be content in catalysts increases, and the formations of isoparafins and isoolefins are inhibited at the same time. The main aromatics formed are xylenes and trimethylbenzenes (or toluene), and their product distributions vary regardless of reaction time and the Be content in catalysts. However, the alkylation selectivity (trimethylbenzenes/xylenes) reduces with the Be content, and the product selectivity in xylene isomers is approximately constant.

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