Abstract
From the field inspection of weathered granitic rocks, we divided them into following five zones; the outermost part with a characteristic of talus and the inner transitional four parts for weathered zone.
The degrees of the alteration of biotite and the production of secondary minerals in the process of weathering are roughly parallel to the degree in progress of weathering. The weathered biotites collected from each zone indicated the variation of basal reflection (001) from 10Å to 11-14Å with production of the hydrous or hydrated minerals such as hydrobiotite and 14Å mineral (vermiculite) and sometimes associated with certain amount of goethite derived from the dissolved iron. A lot of 14Å mineral is Al rich vermiculite. The latest products are the aluminous minerals such as kaolinite and/or gibbsite derived from vermiculite. While in some specimens, kaolinite was recognized in biotite in the initial step of weathering.
