Mineralogy of an Unusual Alteration Product of Kyanite from Karnataka, India

An alteration product of kyanite from Kudinirkatte near Holalkere, Karnataka State, is found to be a hydrous alumino-silicate with a chemical composition corresponding to that of muscovite. Thermal, X-ray diffraction, and infrared spectral data show distinct variation from the known polymorphs of muscovite. On hydrothermal reactions with potassium-rich solution, the alteration product converts to 1M muscovite, and in sodium-rich solution, it converts to a mixture of muscovite and paragonite. When seeded, it converts to 2M muscovite at a higher temperature and pressure. The alteration product of kyanite has a 1M muscovite structure with randomly distributed montmorillonite domains.