Feinglosite, a New Mineral Related to Brackebuschite, from Tsumeb, Namibia

A. M. Clark, A. J. Criddle, A. C. Roberts, M. Bonardi* and E. A. Moffatt
Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8
Canadian Conservation Institute, 1030 Innes Road, Ottawa, Ontario, Canada K1A 0C8
*Present address: I.S.D.G.M., S. Polo 1364, 30125 Venice, Italy

Abstract: 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: Pb2(Zn,Fe)[(As,S)O4]·H2O. Feinglosite is monoclinic, space group P21 or P21/m, a 8.973(6), b 5.955(3), c 7.766(6) Å, β 112.20(6)°, with Z = 2. The strongest five reflections of the X-ray powder diffraction pattern are [d in Å (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.

Keywords: feinglosite • new mineral • brackebuschite group • lead-zinc arsenate hydrate • X-ray data • electron-microprobe data • reflectance data • Tsumeb • Namibia

Mineralogical Magazine; April 1997 v. 61; no. 405; p. 285-289; DOI: 10.1180/minmag.1997.061.405.11
© 1997, The Mineralogical Society
Mineralogical Society (www.minersoc.org)