Mica Weathering Rates as Related to Mica Type and Composition

Abstract

Potassium release rates from micas varying widely in type and composition were measured. A sodium tetraphenylboron solution was used as the extracting agent. Muscovites were found to be two orders of magnitude more stable than a naturally occurring phlogopite and biotite. Synthetic fluorphlogopite was as stable as some muscovites. Lepidolite was the most stable mica. Primary factors affecting mica stability are thought to be: Hydroxyl bond orientation, isomorphous replacement of OH⁻ by F⁻, the stronger Lewis base, and structural factors that lead to compression or stretching of the K—O bond.