The present paper reports the result of researches on the origin and geological occurrence of the Yamagata-bentonite. Two of the deposits, the Oginokubo and the Rokkaku, both located near Yamagata-city, Yamagata Province, were studied in the field and on the geological map, the 29 specimens chemically and microscopically.
(1) Almost of the known Japanese bentonite deposits, as well as acid-clay ones, occur in the Tohoku and Hokkaido regions along the Tohoku volucanic chains.
(2) All of the Yamagata-bentonite belong to greenishyellow species. By later weathering, however, the originally wax-like green bentonite gradually turns pale, yellow, buff and finally pink. The swelling capacity seems to be most developed at the yellow stage.
(3) The bentonite deposit occurs in the older Tertiary, in the vicinity of contact place by later rhyolite through the Tertiary. There are three some distinct types of deposit-(1) agglomerate-tuff-like; (2) complicated alternative-layer-like; (3) small pocket or lens-like. But the third type is of less commercial significance. The closely associated vein rock is exclusively white rhyoritic lava or green vitreous tuff and the bentonite part ranges in size or thickness from few mm to 50cm, rarely, if any, up to 1mm.
(4) The bentonite is a result of devitrification and partial alteration or transformation of trachyandesite-like tuff, yet it seems, with some mouther rock, that the devitrification is not absolutely necessary. In the bentonitization the contact of waterbearing mother ash and high temperature lava or ash is always necessary and enough condition, i.e., the reaction seems to well be proceeded without any hydrothermal or pneumatolytic stuff. A typical bentonite, nearest to mother rock in chemical composition and consisted almost of sericite like flakes, has a pale-yellow wax-like appearance and the following analysis (110°C dry base):
(5) Bentonitization is a kind of propylitization and it seems to bear some resemblance to chloritization, sericitization or pyrophillite-change, i.e., a characteristic reaction to be entitled to “Bentonitization”.
(6) The essential part or bentonite-itself is equivalent in many points, but not fully, to pyrophillite and can be expressed by the formula, Al₂(Si₄O₁₀)(OH)₂⋅Aq (cf. Rept. II). The normal or ideal reaction of bentonitization can be denoted with the following equation, i.e., the ideal mother rock of bentonite is a volucanic glass equivalent in composition to andesine.
(Ab.An)+2H₂O=2(Al₂O₃⋅4SiO₂⋅H₂O)(Na₂O⋅CaO)

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1) Hitherto no fundamental paper has been published in Japan on the warpage of clay ware taking place in firing while it is a basic problem for the improvement of the Japanese pottery and porcelain. Therefore explanations are given on the importance of the study and its scientific significance. Then the general plan and items of the study are described.
2) It is shown that the phenomenon of glost-warpage is closely connected with that of crazing and shivering. The internal stress originating to the discordance of body and glaze produces not only the defects of the latter but the warpage by the elastic deformation of the ware before crazing or shivering takes place. General explanations are given theoretically on the relations among these phenomena.
3) That the stress distribution can be found correctly by determining the thermal expansion, modulus of elasticity, and warpage of body and glaze individually and that the stress can be appropriately calculated from the theory and formulae on the bending of bi-metal are explained.
4) It is explained that the fundamental theoretical equations for the warpage can be derived from the mathematical analysis based on the theory same to the bending theory of bi-metal. Furthermore, as a theoretical analysis of the warpage or central deflection of the test pieces which has been determined in the study, the following equation has been derived for the approximate relation among the warpage δ, the thickness of glaze h₁, that of body h₂, the coefficient of the thermal expansion of the glaze α, that of the body β, the modulus of elasticity of the glaze E₁, that of the body E₂, the length of the test piece l, and the temperature difference which takes place while solidified glaze cools to room temperature θ:
δ=l²(α-β)θ/4[1/3{E₁h₁³+E₂h₂³/h₁+h₂}{1/E₁h₁+1/E₂h₂}+(h₁+h₂)]………(7)
An approximate theoretical equation has also been given for the internal stress P, compression or tension, as follows:
P=b{(α-β)θl²-4δ(h₁-h₂)}E₁E₂h₁h₂/l²(E₁h₁+E₂h₂)………(8)
Where b is the breadth of the test piece.

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