Biehlite, (Sb,As)(2)MoO6, a new mineral from Tsumeb, Namibia

Biehlite, a new diantimony molybdenum hexaoxide, ideally (Sb,As)(2)MoO6, is monoclinic, space group C2/c, with a = 18.076(5) Angstrom, b = 5.920(5) A, c = 5.083(5) Angstrom, beta = 96.97 beta degrees (1), Z = 4, cell volume 5 39.91 Angstrom(3), from single crystal studies. The strongest reflections i n the X-ray powder diffraction data are (d(mea)s., I, hkl) 5.622 (65) (110) , 3.376 (39) ((3) over bar 11), 3.104 (61) (311), 2.990 (100) (600), 2.960 (100) (020), 2.104 (42) (620). Biehlite was found in the Tsumeb mine, Tsume b, Namibia. It forms long white flexible fibreous crystals which are only s ome microns in diameter. The fibres build up irregular aggregates and Felty mosses in association with anglesite and wulfenite. Electron microprobe an alyses give Sb2O3 60.99, As2O3 4.95, MoO3 33.76, total 99.70 wt.%, leading to an empirical formula of (Sb-1.79(3+), As-0.21(3+))Mo6+ O-1.00(6).