Feinglosite, a new mineral related to brackebuschite, from Tsumeb, Namibia

Feinglosite, the zinc analogue of arsenbrackebuschite, was found lining a cavity in a sample of massive chalcocite from Tsumeb, Namibia. In this cavity it is associated with wulfenite, anglesite and goethite. The 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. The strongest five reflections of the X-ray powder diffraction pattern are [d in Angstrom (I) (hkl)]: 4.85 (50) (110), 3.246 (100) (112), 2.988 (60) (301), 2.769 (60) (300/211), 2.107 (50) (321). The mineral is pale olive-green, transparent, sectile, and has a white streak and adamantine lustre. It overgrows clusters of goethite crystals and forms globular microcrystalline aggregates up to 0.5-0.75mm in size. The hardness 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 pale brownish grey in reflected light (when compared with goethite). Visible spectrum reflectance data are presented. Feinglosite is named for Mark N. Feinglos who first recognised the mineral on a specimen in his collection.