a new refractory mineral from the Allende meteorite
Chi Ma & George R. Rossman
Division of Geological
and Planetary Sciences
California Institute of Technology
Pasadena, CA 91125-2500, USA
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
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+1.90Mg0.07Al0.01Zr0.01)Σ2.02O3.
Tistarite is rhombohedral, R-3c; a = 5.158 Å, c = 13.611
Å, V = 313.61 Å3, and Z = 6.
Its electron back-scatter diffraction pattern matches that of synthetic
with the R-3c 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.
Reflected light photomicrograph of tistarite
that has its top half with a residual coating of carbon after the
electron microprobe analysis.
Backscattered electron image of the same
tistarite in the SEM.
American Mineralogist 93, 154-157