Mahadevite-a new species of mica

Abstract

The physical properties and chemical composition of a species of mica from the Warangal district in Hyderabad have been studied. Thick sheets are bronze-coloured and opaque, while thin sheets transmit light of a greenish yellow tint, the pleochroism being weak but distinct. The optic axial angle is 13° 48'. Th plane of the optic axes is perpendicular to the plane of symmetry. The composition is SiO₂ 38·98%, Al₂O₃ 29·94%, Fe₂O₃ and FeO 4·12%, Mgo 13·2%, K₂O 9·6% water 3·8%. On the basis of Pauling’s model of the mica structure, the numbers of atoms of various elements in six, and twelve co-ordination positions are calculated. Approximately equal number of Al and Mg atoms are found in six co-ordination. The mica appears to be of a type intermediate between muscovite and phlogopite.