Abstract
Twelve profiles of ferralitic soils derived from different igneous rocks were collected from hilly and mountainous areas in the Northern, North of Central, Coastal Area of Southern Central and High Plateau Tay Nguyen regions of Vietnam, and were subjected to clay mineral analysis. The main clay minerals detected were kaolin (kaolinite and halloysite (0.7nm)), 2: 1-type silicate (mainly mica, vermiculite, smectite, the mica/vermiculite/smectite-mica/smectite mixed-layer mineral, and chlorite-vermiculite intergrade), and oxide/hydroxide (gibbsite and goethite) minerals. Based on the abundance of kaolin and oxide/hydroxide minerals in the clay fraction, twelve profiles were grouped into 3 groups. The mineralogical difference of soils among the three groups was explained by the difference in rock-forming minerals of igneous rocks rather than by advancement of ferralitization, different from soils derived from sedimentary and metamorphic rocks in the previous study (Nguyen and Egashira, 2007). Inherent potentiality of the soils was assessed based on the type and amount of clay minerals and varied with soils depending mainly on the amount of 2: 1-type silicate minerals in the clay fraction.
