Relation between the Parent Materials and Clay Minerals in the Soil of Mt. Katasone, Fukushima Prefecture (Part 2) : Mineral Composition of the Clay Fraction

Abstract

1. The soil profile is formed from the weathering product of granodiorite covered by the mixture of hornblende gabbro and ash of dacite, and also by that of hornblende gabbro, ash of dacite and ash of pyroxene andesite. 2. The occurrence of minerals of montmorillonite group, hydrated-halloysite and kaolinite in the soil is clearly shown by X-ray powder photographs. 3. The cation-exchange capacities are about 50m.e. except in the fraction of No. 9,0.5〜1.0μ, but the molecular SiO_2/Al_2O_3 ratios are about 2.5 in those fractions, which seem to contain much of the minerals of montmorillonite group from the results of X-ray powder photographs. These facts indicate that the mineral of montmorillonite group may be beidellite. 4. The differential thermal curves clearly show the occurrence of beidellite, hydrated-halloysite and kaolinite. A small amount of montmorillonite may be contained. 5. The translucent and the opaque minerals, which appear on the electron micrographs, seem to be beidellite and hydrated-halloysite or kaolinite respectively. 6. The occurrence of beidellite, hydrated-halloysite and kaolinite in the soil is proved by these experiments. A small amount of montmorillonite may be contained in some fractions. 7. It is distinct that in the profile kaolinite is formed in relation to the granodiorite, and beidellite and hydrated-halloysite, to the hornblende gabbro and the two kinds of volcanic ash. Hydrated-halloysite is formed from volcanic ash in general in the soils in Japan, and the minerals of montmorillonite group seem to be formed at the environment rich in bases. From these facts, beidellite seems to be formed in relation to the hornblende gabbro, and hydrated-halloysite, to the two kinds of volcanic ash. Lastly, it must be added that some of the clay minerals, have been called beidellite, are shown by GRIM and others to be a mixture in which illite is an important component, or a mixed layer aggregate of montmorillonite and illite.