Tuite, gamma -Ca (sub 3) (PO (sub 4) ) (sub 2) ; a new mineral from the Suizhou L6 chondrite

Tuite, gamma -Ca (sub 3) (PO (sub 4) ) (sub 2) , the high-pressure polymorph of whitlockite, was found in a shock melt vein of the Suizhou chondrite. It occurs as polycrystalline aggregates in association with coarse-grained aggregates of ringwoodite, majorite and NaAlSi (sub 3) O (sub 8) -hollandite. These high-pressure mineral assemblages are enclosed in the fine-grained matrix of the vein that consists of majorite-pyrope (sub ss) garnet, metal and troilite. This new mineral is trigonal, R3m, a = 5.258 Aa, c = 18.727 Aa. The tuite is colourless and transparent with vitreous lustre and white streak; it is uniaxial (+) with high refractive indices (epsilon = 1.706, omega = 1.701) and low birefringence (0.005). Microprobe analyses of tuite yield an empirical formula (Ca (sub 2.51) Mg (sub 0.29) ) (sub 2.80) Na (sub 0.28) (P (sub 1.01) O (sub 4) ) (sub 2) . The simplified formula, Ca (sub 3) (PO (sub 4) ) (sub 2) , is the same as whitlockite outside the veins. Stronger reflections on synchrotron radiation X-ray powder diffraction pattern of tuite are d = 2.628 (100), 2.891 (80), 1.945 (47), 1.730 (25) and 1.567 (22). The figures in brackets are relative intensities. Tuite in the shock vein of this meteorite was transformed from whitlockite via a shock-produced solid-state reaction, while the pressure and temperature in the shock vein attained 23 GPa and 2000 degrees C. This new mineral and the mineral name (tuite) have been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association.