Abstract
The weathering process of a granitic rock was mineralogically investigated with XRD, XRF, SEM and TEM at one weathered profile (Ca. 20m in height) in the western part of Cameroon where climate is the intermediate of humid and arid tropical condition. Halloysite and kaolinite are main constituent clay minerals in the granite saprolite (weathered granite). Halloysite predominantly occurs at the lower part of the investigated profile associating with small amount of kaolinite. Numerous spherical-shaped halloysite were observed in the bottom of the profile under TEM. The granite saprolite at the top part of the profile consists mainly of platy kaolinite with small amount of tubular halloysite.
Detailed observation of morphological variation by TEM together with X-ray analysis revealed that the spherical-shaped halloysite crystals (0.05-0.5μm) are first unrolled and then transform to tubular halloysite (0.05-2μm), and finally unrolled again producing platy kaolinite (0.2-3μm). Close relationship between crystal size and morphology is obtained.
