Clay Mineral Formation from Pumice in Volcanic Ash Soils of Japan

Abstract

The weathered pumice, 100-200μ in size, separated from the soil samples, broke down into fine particles on the treatment of deferration. Several size fractions fractionated from these particles by sedimentation were mineralogically studied by X-ray diffraction analysis.
1) In the younger soils pumice is an unweathered glass with a small amount of montmorillonite.
2) As weathering proceeds, 14Å clay minerals with small amounts of illite and 7Å kaolin mineral increase. The aluminum interlayering becomes enhanced.
3) Montmorillonite mainly exists in the fine fraction. The aluminum interlayering of 14Å clay minerals tends to increase with increasing of particle size. Illite and kaolin mineral are dominant in the coarser fraction.
4) A 7Å kaolin mineral increases slightly as weathering proceeds. Halloysite is not present.
These results which are identical with the clay mineral properties of volcanic ash soils reported by the authors, seem to indicate that the 14Å clay minerals are not the derivative of some mafic minerals, but the weathering products of all the parent materials.