3T polytype of an iron-rich oxyphlogopite from the Bartoy volcanic field, Transbaikalia: Mössbauer, infrared, Raman spectroscopy, and crystal structure

The Mossbauer, infrared and Raman spectra of iron-rich oxyphlogopite from a new locality, the Bartoy occurrence, Transbaikalia, Russia were obtained and its crystal structure was solved. The mineral is characterized by the absence of OH groups and ordered distribution of Fe2+ and Fe3+ between sites having octahedral coordination. Unlike oxyphlogopite holotype sample which is monoclinic (1M polytype), iron-rich oxyphlogopite belongs to the 3T polytype (space group P3(1)12) with the unit-cell parameters a = 5.3248(2) angstrom, c = 29.788(3) angstrom, V = 731.44(8) angstrom(3). Its refined crystal-chemical formula is (Z = 3): (A)(K0.9Na0.1) [(M1)(Fe0.62+Mg0.4) (M2)(Fe0.43+Ti0.4Mg0.2) (M3)(Mg0.4Fe0.33+Ti0.2Al0.1)] [(T1,2)(Si0.7Al0.3)(2)O-5](2)(X)(O0.9F0.1)(2).