Weathering of biotite in the Daito granodiorite, Shimane Prefecture, Japan.

The alteration sequence of biotite in granitic rocks at two weathered profiles (Kisuki and Yamakata) located in Shimane Prefecture was investigated. The weathering condition in this district was also inferred from the results. The alteration products from biotite were hydrobiotite, vermiculite, kaolinite, goethite and gibbsite. The main alteration sequence of biotite in the weathered granite of this district has been assumed as follows: biotite→hydrobiotite→vermiculite→kaolinite Biotite grains were treated with several solutions (pH 3.0, 5.3, 8.0) at 60°C for 55 days. It is assumed in comparison with the experiment and the alteration of biotite in some other district that biotite in this studied district was altered under the temperate condition such as recent climate in this district.