The crystal structure of synthetic MgIVmica

The crystal structure of a mica, which was synthesized from talc and potassium carbonate under a hydrothermal condition, was determined by least- squares methods. The mica is a Mg-rich free from Al ions, with Mg ions substi- tuting for Si, and with some vacant positions in the octahedral sites. This mica is intermediate between the trioctahedral and dioctahedral types and agrees with a Mg-rich mica first reported by SEIFERT and SCHREYER (1971). The lattice parameters are: a = 5.321(2), b = 9.238(1), c = 10.287(1) A andp = 100.06°(1). The space group is 02/m with Z = 1. The final residual is R = 9.20/0 using anisotropic temperature factors. The refinement gave the structural formula: