In Gotsu district, central part of Shimane Prefecture, highly weathered reddish plutonic rocks are developed. These reddish weathered crusts in part underlie the Plio-Pleistocene Tsunozu formation. Main mineral compositions of the reddish weathered crust are kaolin and vermiculitic mineral.
Undoubtedly these reddish weathered materials must have been formed under much warmer climatic circumstances during late Pliocene judged from the stratigraphical relation of the weathered crust to the Tsunozu formation. Not only climatic condition and physiographic features but also chemical and physical properties of the rocks take part in the weathering processes.
In this study, the writer proposes a “degree of the absolute chemical freshness” based on the following empirical formula:
Degree of the absolute chemical freshness
FeO+MnO+MgO+CaO+Na₂O+K₂O/Al₂O₃+Fe₂O₃+H₂O (+) (Weathered rock) /FeO+MnO+MgO+CaO+Na₂O+K₂O/Al₂O₃+Fe₂O₃+H₂O (+) (Fresh rock)
This formula is applicable to the applied geological works.