Journal of the Indian Society of Soil Science

In the old alluvial soils representing Dulhingaon, Agiaon, Kapsandi and Suhiya series (Psammentic/Udic Haplustalfs and Typic Haplusterts) which have developed on alluvium derived from the rocks like granite-gneiss, basalt, quartzite, etc., the clay minerals seem to be geogenic and pedogenic. The dominance of kaolinite in upland soils of Dulhingaon series may be due to their acidic and well drained environment, while illite in the soils of Agiaon series is due to high K content. Mica and hydrous mica are found to be derived from feldspars. A portion of kaolinite seems to be inherited from the parent material. Some of the orthoclase feldspars appear to have weathered to kaolinite. The formation of smectite appears to be under basic environment, impeded drainage and waterlogging.