Letter. Tistarite, Ti₂O₃, a new refractory mineral from the Allende meteorite

Abstract

Tistarite, ideally Ti₂O₃, is a new member of the corundum-hematite group. It is found as one subhedral crystal in a cluster of micrometer-sized refractory grains along with khamrabaevite (TiC), rutile, and corundum crystals within a chondrule from the Allende meteorite. The mean chemical composition determined by electron microprobe analysis is (wt%) Ti₂O₃ 94.94, MgO 2.06, Al₂O₃ 1.50, ZrO₂ 0.44, FeO 0.24, CaO 0.10, Cr₂O₃ 0.06, sum 99.34. The empirical formula calculated on the basis of 3 O atoms is (Ti³⁺ _1.90Mg_0.07Al_0.04Zr_0.01)_Σ2.02O₃. Tistarite is rhombohedral, R3̄c; a = 5.158 Å, c = 13.611 Å, V = 313.61 ų, and Z = 6. Its electron back-scatter diffraction pattern matches that of synthetic Ti₂O₃ with the R3̄c structure. The strongest calculated X-ray powder diffraction lines from the synthetic Ti₂O3 data are [d spacing in Å (I) hkl]: 3.734 (84) (012), 2.707 (88) (104), 2.579 (90) (110), 2.242 (38) (113), 1.867 (33) (024), 1.703 (100) (116), 1.512 (28) (214), 1.489 (46) (300), 1.121 (20) (226), 0.896 (25) (416). The mineral is named after the composition “Ti” and the word “star,” implying that this new refractory mineral is among the first solids formed in the solar system.