| Photo of granite exposure |
| In the first photo you can see a competent, non-weathered granitic rock. In the second photo you can see a slope of granitic rock. In this outcrop the ruptures were filled with caolinite and appeared very white. The granitic rock contains also biotite (mica) as proven by the fact that the black minerals could be scratched and flake. The chemical composition of the granitic rock contains probably very small quantities of iron since the weathered material looks so white. The outcrop is very susceptible to erosion because it is not cohesive and has been under deep chemical weathering. During this procedure the feldspar weathered to clay (caolinite) and the biotite also weathered to caolinite. These minerals, during weathering, expand and the rock fractures more enhancing that way the weathering procedure. The final material is called saprolite. This is of importance because while drilling an exploration borehole into saprolite, the driller may find corestones, which are totally unweathered blocks. This fact may lead the geologist in considering that point as the depth of the “hard” rock. Exploration must continue for at least 5-10ft (1.5-3.5m)to verify that the bedrock was found. |
| References: Information collected during the field trip in the Sierra Nevada, as part of the "Engineering Geology" course curriculum, instructed by Professor N. Sitar, Department of Civil & Environmental Engineering, University of California at Berkeley. |
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