National Bureau of Soil Survey and Land Use Planning, Amravati Road, Nagpur, 440010.
Present address:1 Krishi Anusandhan Bhavan, JARI Campus, New Delhi.
Three representative pedons developed over charnockite, laterite and weathered gneiss under hot humid to perhumid environment (Agro-ecoregion-AER NO.8 and 19) of Kerala were examined for morphological, mineralogical and physicochemical properties to study the mineral weathering in soils and to group them in different classes. The high amount of easily weatherable minerals such as biotite, hypersthene and hornblende in soils developed over charnockite and granitic-gneiss and of opaque mineral assemblages in the heavy mineral fractions of soils developed over laterite, indicate that these soils differ in evolution and the former is comparatively younger in age. The biotite observed in the soil possibly derived from the probable parent materials viz. granitic- and biotite-gneiss. The ferruginous coating over the surface of biotite prevents further alteration. The other minerals. such as hornblende and hypersthene observed in the heavy sand fraction of soils might have been derived from the country rocks, such as charnockite and hornblende gneiss. The X-ray analysis of minerals in the clay fractions of soil indicates the dominance of kaolinite possibly due to intense kaolinisation in the finer fractions of biotite.
Heavy mineral, weathering, kaolinisation
