Zhangpeishanite, BaFCl, a new mineral in fluorite from Bayan Obo, Inner Mongolia, China

摘要

Zhangpeishanite, ideally BaFCl, occurs as inclusions up to 100 μm across in fluorite from Bayan Obo, Inner Mongolia, China. It is associated with barite, hematite and norsethite in fluorite. Zhangpeishanite occurs as transparent, colourless crystals with a white streak and vitreous luster. It is tetragonal, P4mm, a = 4.3951(8), c = 7.223(2) ?, V = 139.52(7) ?3, Z = 2. The five strongest lines in the powder XRD pattern are [d(?), I/I0, hkl]: (3.75, 100, 101), (3.11, 94, 110), (2.36, 82, 112), (2.79, 67, 012) and (1.898, 49, 211). The mean of twelve electron-microprobe analyses is (wt.%); Ba 70.90, F 9.88, Cl 18.85, and leads to the empirical formula Ba0.99F0.99Cl1.02 on the basis of 3 apfu. Zhangpeishanite is a member of the matlockite group (Struntz-Nickel grouping 3DC.25), the Ba-dominant analogue of matlockite and rorisite. The calculated density of zhangpeishanite is 4.54 g/cm3. Zhangpeishanite is non-fluorescent. The hardness is 2? on Mohs' scale (measured on a synthetic equivalent). The optical data obtained from the synthetic equivalent are: uniaxial ( - ), ω = 1.656(2), ε = 1.652(2) (589 nm).