The flow characteristics for 2.5%dispersions of smectites were investigated by a continuous and variable rpm viscometer of concentric-cylinder type. The smectite samples used were a purified bentonite product Kunipia-F, a synthesized hectorite-like clay product Laponite RD and a fluorhectorite-like clay specimen FH-03 hydrothermally synthesized at 150°C in 2 h. The flow curve for the Kunipia-F dispersion was essentially the same as those for colloidal coagulated sols, and could be accounted for by two parameters, plastic viscosity and yield value. On the other hand, shear rate and shear stress flow curves for 2.5% dispersions of RD and FH-03 showed mountain-shaped parts caused by their gel formation. Peak positions of the mountain-shaped parts were time-dependent. After a short set time, a first peak appeared at 40 s^-1, then an additional peak followed at 119 s^-1 as the set time became longer, and ultimately the first peak tended to disappear. This may indicate that both RD and FH-03 gels were formed in two stages. The differences of flow characteristics between RD and FH-03 dispersions are summarized as follows;
(1) The mountain-shaped parts in the flow curves for FH-03 dispersions appeared faster than that for RD dispersion, implying that FH-03 dispersion formed gel structure more quickly compared with RD dispersion, (2) The hysterisis loop area in the flow curve for FH-03 dispersion was larger than that for RD dispersion, indicating that FH-03 dispersion has higher thixotropic nature than RD dispersion, (3) The hysterisis loop was divided into two areas, one responsible for the gel structure and the other for the coagulated sol structure. The former was dominant in FH-03 dispersion and so was the latter in RD dispersion.

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Andesite dike and andesite sheet intrude the gravel beds of Kuma Group in the Tobe district, Ehime Prefecture. They are altered to pottery stone by hydrothermal activity. The pottery stone depostits in the Mannen and Uebi areas are typical.
The pottery stone deposits of the areas consist generally of abundant quartz with some amounts of clay minerals such as interstratified mica/smectite minerals, tosudite, kaolinite, and so on. Alteration zoning in the deposits is possible on the basis of the clay mineral assemblages. The dike type deposit in the Mannen area shows a zonal arrangement in which the central zone consists of interstratified mica/smectite minerals with g=3 and P_M>0.9 and the outer zone, the same minerals with g=3-2 and P_M>0.8 and kaolinite, as the major minerals, where g denotes “Reichweite” and PM, the probability of occurrence of mica layer. On the other hand, the sheet type deposit in the Uebi area shows a transition of major mineral constituents, from the bottom upward, from tosudite to tosudite plus interstratified mica/smectite minerals with g=1 and P_M=0.5 and then to interstratified mica/smectite minerals with same values of g and P_M. Kaolinite is a common constituent in all the bottom, intermediate and top zones and enriched in the hanging sides, in the latter case.
The mechanism of hydrothermal alteration which has possibly been related genetically to the formation of pottery stones in the study areas may be explained on the basis of theoretical and empirical considerations as follows: It is a general rule that the stoichiometric solubility of quartz decreases, and that of the usual silicate, oxide and hydroxide minerals increases with the decrease of temperature ofhydrothermal systems at a fixed pH. Also, stoichiometric solubility of the usual rock forming minerals is much larger than that of the clay minerals which have the similar chemical composition, so that the latter are probably deposited with dissolution of the former. Therefore, when a hydrothermal solution which has been equilibrated with quartz and other minerals in a host rock is cooled by its ascension, quartz is probably the main product with some clay minerals, and some other minerals often remain as relicts. Glass tends to disappear more rapidly than the crystalline minerals from the path of hydrothermal solutions, because of its relatively high solubility. Adoption of the above reasoning to the pottery stones under the present study may be justified by the presence of idiomorphic quartz particles and various clay minerals in them, together with the observed porous structure of them. Incidental calculation made on the the solution in a model aquifer which is in equilibrium with various minerals indicated that quartz and muscovite are precipitated and feldspars dissolved when the solution composition is changed by temperature drop.
Another reaction is assumed to have occurred simultaneouly during the formation of pottery stones in the study areas, as follows: Ground water which had been saturated with oxygen during the movement through the gravel bed diluted the hydrothermal solution and thereby oxidized the sulfides, such as HS-and H₂S, to sulfate. The mixed solution became weakly or strongly acid depending on the extent of the dilution as well as the amount of the sulfides originally present. It is natural to assumethat the dilution was limited rather to the outside of the rock body in the case of dike type (Mannen area), and was spread over the whole rock body in the case of sheet type (Uebi area) intrusion.

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Clay minerals are solid acids with Brφnsted and/or Lewis acid sites. The Brφnsted acidity arises usually from the permanent negative charge sites, the exchangeable cations with hydration shell (hydrated Lewis acid), and the silanol groups located on the broken edges, etc., and the Lewis acidity from the exchangeable cations, such as Al, Fe, and Mg, exposed at the broken edges. With such acidities together with large surface areas, clay minerals, especially montmorillonite, have long been used as catalysts for organic reactions, such as oxidation, addition, dehydration, and polymerization. In recent years, much attention has been drawn into the catalytic ability of pillared clay minerals and their acidities.

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