Abstract
The Daito granodiorite mass is widely exposed in Kisuki-Daito district. This rock has a somewhat homogeneous composition and is medium to coarse-grained rock consisting chiefly of plagioclase, quartz, orthoclase, biotite and hornbelnde, accompanied by small quantites of apatite, magnetite, zircon and sphane.
Whole rock and their biotite were examined by X-ray powder diffraction method and chemical analysis.
The grade of chemical weathering that have taken place in rocks was determined by A.D.F. proposed by present writer.
The amount of leaching from the parent rocks, relating to the cation, have intimate relations with A.D.F.
By weathering reaction, biotite is altered to the mixed matters composed of biotite and kaolinite at about 15 in A.D.F., passing through the mixed matters composed of unstable biotite, interstratified biotite-vermiculite mineral and kaolinite at about 89, interstratified vermiculite-montmorillonite mineral, interstratified biotitevermiculite mineral and kaolinite at about 77, interstratified biotite-(vermiculitechlorite intergrade) mineral and kaolinite at about 19 in A.D.F. value.
The results indicates that the altered products of biotite gives a measure of the proceeding on the weathering process of parental rock.
