Weathering of Sodium‐Potassium Mica in Soils of the Virginia Piedmont

Abstract The occurrence of paragonite, the Na‐analogue of muscovite, in intimate association with muscovite was observed in two soils and their parent materials in the Virginia Piedmont. A relatively constant Na/K molar ratio of approximately 1 was maintained in both the parent rocks and soils. This indicated that equal molar quantities of paragonite and muscovite were present and that the weathering rates of the two micas were similar. Vermiculite and kaolinite were the weathering products formed upon weathering of the mixed Na‐K mica. The vermiculite had the same expansion and contraction characteristics as that formed from a predominantly K‐mica. Consequently, the kind of weathering of muscovite and paragonite also appears to be similar. Paragonite is believed to be of more widespread occurrence than previous work has indicated. Its possible influence on soil genesis, morphology, and classification may be significant.