Nobuo Uchiyama

Montmorillonite in a Volcanic Ash Soil

Abstract Many kinds of volcanic ash soil distributed in Japan are usually high in humus content, consequently very dark or nearly black in color, light, loose and very friable. They have also a marked allitic property owing to the relatively large contents of allophane and aluminium hydrous oxide which strongly bind with phosphate ion.

Crystalline clay minerals of the soils derived from recent volcanic ashes in Hokkaido, Japan: II. 2:1 Type Clay Minerals

Abstract In the previous study on clay minerals in the soils derived from recent volcanic ashes, it has been shown that expanding layer silicates with more or less interlayer-Al are found in large amounts among crystalline clay minerals, and that chlorite, illite and possibly kaolin minerals are found in small amounts (1). Montmori11onite shows a tendency to be dominant in the soils of the younger group and to be less Alinterlayered, However, vermiculite tends to increase, and both montmorillonite and vermiculite become more Al-interlayered in the soils of the older group. The purpose of the present report is to investigate 2: 1 type clay minerals, chiefly expanding layer silicates.

Discussion on Al-substitution in tetrahedral-layer and its relation to the contents of MgO and K2O of mica minerals

Abstract Magnitude of Al-tetrahedron in Mica-type Minerals Mica and mica-type minerals are composed of two Si-tetrahedral layers and one octahedral layer sandwiched between the former two. In the lattice structure of these minerals, tetrahedral layers are constructed from hexagonal assemblages of tetrahedrons formed by four oxygen atoms and a cation. In a cavity at the center of the tetrahedron formed by four oxygen atoms a cation such as Si or AI can fit in and balance negative charges of oxygen. However, the cations are limited to those whose crystal radii are not so large as to weaken the O-O linkage between two neighbouring tetrahedrons. Consequently, Sitetrahedron or Al-tetrahedron can only exist in actual minerals. The magnitude of these tetrahedrons may be considered to be proportional to the crystal radii of the cations.