Toturite Ca3Sn2Fe2SiO12--A new mineral species of the garnet group

A new Sn-rich garnet, toturite Ca 3 Sn 2 Fe 2 SiO 12 , occurs as an accessory mineral in high-temperature altered carbonate-silicate xenoliths in ignimbrite of the Upper Chegem structure in the Northern Caucasus, Kabardino-Balkaria, Russia. The empirical formula of toturite from the holotype sample is (Ca 2.989 Fe 2+ 0.011) Σ3 (Sn 4+ 1.463 Sb 5+ 0.325 Ti 4+ 0.193 Zr 0.013 Mg 0.003 Nb 5+ 0.002 Cr 0.001 ) Σ2 (Fe 3+ 1.633 Al 0.609 Si 0.552 Ti 4+ 0.166 Fe 2+ 0.039 V 5+ 0.001 ) Σ3 O 12 . The mineral forms thin regular growth zones and irregular spots in the Fe 3+ -dominant analog of kimzeyite. Toturite is cubic, Ia3̅d, a ≈ 12.55 Å, as is confirmed by electron backscatter diffraction (EBSD) data. The strongest lines of the calculated powder diffraction pattern are [d, Å (hkl) I]: 2.562 (422) 100, 1.677 (642) 91, 3.138 (400) 74, 4.437 (220) 67, 1.146 (10.4.2) 31, 1.046 (884) 25, 1.984 (620) 23. Raman spectra of toturite are analogous to those of kimzeyite and shows the following diagnostic bands (cm -1 ): 244, 301, 494, 497, 575, 734. The association of toturite with larnite, rondorfite, wadalite, magnesioferrite, lakargiite, and cuspidine indicates a high temperature (>800 °C) of formation. The mineral name is given after the Totur River situated in Eltyubyu village, also Totur is the name of a Balkarian god.