FEINGLOSITE, A NEW MINERAL RELATED TO BRACKEBUSCHITE, FROM TSUMEB, NAMIBIA

Feinglosite, the zinc analogue of arsenbrackebuschite, was found linin g a cavity in a sample of massive chalcocite from Tsumeb, Namibia. In this cavity it is associated with wulfenite, anglesite and goethite. T he mean of seven electron-microprobe analyses (wt.%) is: PbO 61.4, ZnO 7.3, FeO 1.8, As2O5 22.1, SO3 5.3, H2O (by difference) [2.1], total = [100.00]%, leading to the ideal formula: Pb-2(Zn,Fe)[(As,S)O-4]. H2O. Feinglosite is monoclinic, space group P2(1) or P2(1)/m, a 8.973(6), b 5.955(3), c 7.766(6) Angstrom, beta 112.20(6)degrees, with Z = 2. Th e strongest five reflections of the X-ray powder diffraction pattern a re [d in Angstrom (I) (hkl)]: 4.85 (50) (110), 3.246 (100) (112), 2.98 8 (60) (301), 2.769 (60) (300/211), 2.107 (50) (321). The mineral is p ale olive-green, transparent, sectile, and has a white streak and adam antine lustre. It overgrows clusters of goethite crystals and forms gl obular microcrystalline aggregates up to 0.5-0.75mm in size. The hardn ess on Mohs' scale is 4-5: the mean micro-indentation hardness is 263 at VHN100. Its calculated density is 6.52 g cm(-3). The mineral is pal e brownish grey in reflected light (when compared with goethite). Visi ble spectrum reflectance data are presented. Feinglosite is named for Mark N. Feinglos who first recognised the mineral on a specimen in his collection.