Clay mineralogy of the saprolite of some volcanic rocks in Japan

Abstract

The relation of the clay mineralogical composition to the parent rock was investigated on the saprolite of several volcanic rocks which were collected from Gunma. Iwate, Kagawa, Nagasaki, and Oita prefectures. Gibbsite, illite, chlorite, vermiculite, and montmorillonite were predominant in the saprolites containing quartz In the groundmass, while halloyslte and/or metahalloysite were abundant in the saprolite' with cristobalite and tridymite. The relationship was very sitnilar to that between the clay minerals and the dominant silica minerals in volcanic ash soils in Japan. The silica polymorph in the volcanic materials suggests some differences In the nature of the groundmass or of its equivalent portion of volcanic materials, which result in the formation of different clay minerals.