Clay Minerals of Argiustolis Upper Southwestern Mountainous Region, Saudi Arabia

Abstract

Soil of Argiustolls associate some stable landscapes formed son chlorite schist within upper southwestern mountainous region. Soil profiles are deep and have marked horizonation as the following sequence: mollic epipedon, argillic horizon and soil parent material. The clay mineral assemblages of these soils are mainly chlorite, kaolinite. smectite, vermiculite and traceable amount of hydrous mica associating surface horizons. Most of smectitc minerals were detected in the fine clay of soil solum with maximum amounts at Bt horizons. Coarse clay is dominated by kaolinite and chlorite whereas smectite and vermiculite are in traceable or low amounts. Chlorite is relicts of the parent rock. It is distinctively higher in C horizons and decrease in A and Bt horizons. The decrease of chlorite in soil solum coincides with marked increase in both kaolinite and 2:1 layer lattice clay rninerals. The latter could be considered as intermediate phase through the kaolinization process during alteration and degradation of chlorite. Differences in mineralogical composition between horizons of soil profiles are partly ascribed to pedogenesis