On the crystal structure of biotites

Abstract

The crystal structure of six biotite specimens has been studied by means of one-dimensional Fourier projections on c *. The mean tetrahedral rotation is about 10° for biotites. The K + ion shows an almost regular octahedral coordination with an average K–O bond distance of 2.92 Å. Layer separation around K + has a mean value of 3.37 Å. The Si–O tetrahedra are rather regular. The structural model for the biotites is very close to the recently described structures of muscovite and phlogopite.