Two kinds of typical “acid clay”, treated with 3 parts of boiling 5-45% sulfuric acid for 4 hours, were examined by X-ray powder analysis, chemical analysis, cation exchange capacity, exchangeable hydrogen ion by treatment of 1 N NaCl solution, specific surface area and solid acidity.
One of the samples is of montmorillonite and another is of halloysite. By the acid treatment octahedral layer of the “acid clay” is attacked and cation is leached. Specific surface area of the acid-treated clay increases with increasing concentration of sulfuric acid. It is concluded that the collapse of octahedral layer of the clay enhances the amount of free amorphous silica. The acid-treated clay of montmorillonite is characterized by the solid acidity which is stronger and higher than that of the acid-treated clay of halloysite. This solid acidity varies with the concentration of sulfuric acid and shows maximum value at 15-25% sulfuric acid. The montmorillonite structure left in the residue after acid treatment is assumed to be responsible for this result. It is concluded that the character of the solid acid of acid-treated clay plays an important role in the refinment of aromatic hydrocarbons and the color formation of pressure-sensitive recording paper.

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Kaolin group clay minerals occur as various degree of crystallinity: the lowest is called allophane and one of the highest is called nacrite. Structural investigations of allophane, halloysite, kaolinite, nacrite and metakaolin reported by the present author have summarized as well as literatures by others.

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Surface weathering of the Sambagawa crystalline schists distributed in the Kito-Munemori landslide area, Tokushima Prefecture is characterized by the formation of red solis which is palaeosols formed under the warm and humid climate of Dilvium age. Many kinds of secondary clay minerals are found in the weathered crystalline schists and clay minerals with increasing grade of weathering appear as follows: Black schists
Sericite→Sericite/Al-vermiculite→Al-vermiculite→Kaolin Green schists including chlorite shist
Chlorite→Chlorite/vermiculite→Smectite vermiculite→Al-vermiculite→Kaolin

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As the basic data for differential grinding of weathered granite, the compressive strength of quartz, orthoclase and plagioclase particles was investigated in relation with the argillization of these minerals by weathering process.
Following facts were obtained:(1) Compressive strength of quartz particles shows almost the same value to that for the particles separated from the samples of the different weathering degrees.(2) Strength of strongly weathered orthoclase particles decreases to nearly a half value of the strength for less weathered ones.(3) Compressive strength of plagioclase particles decreases almost one 60 th by weathering.

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Various monoionic montmorillonites were treated with an ethanol solution of O-(PToluenesulf onamido) aniline (abber. TSA) which is a highly specific reagent for precipitating cupric-chelate. These montmorillonite specimens were immersed in the ethanol solution of TSA for 4-5 days, and then air-dried. After this treatment, monoionic montmorillnites saturated with H⁺, Fe³⁺, Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Mg²⁺and Sr²⁺ did not show remarkable change in their basal spacings (14.0-15.4 Å), whereas Cu²⁺ saturated one clearly gave a basal spacing of 21Å under the condition of 0.3 g TSA/1 g specimen. These results indicate that the formation of the complex of montmorillonite-TSA having a 21Å spacing is due to the specificity of TSA. The authors inferred the structure of the complex having an upright orientation of TSA-assemblage in an interlayer, of montmorillonite.

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