, a new mineral species from Tsumeb, Namibia, and associated new gallium analogues of the alunite - Jarosite family
Gallobeudantite, ideally PbGa3[(AsO4),(SO4)]2(OH) 6, is the newly defined Ga analogue of beudantite. It occurs as zoned rhombohedra, up to 200 μm along an edge, in vugs in a single specimen of massive Cu-bearing sulfides from Tsumeb, Namibia. Gallobeudantite is variably pale yellow, greenish, or cream-colored, with a white to pale yellow streak, vitreous luster, even to conchoidal fracture, hardness of 4, and D(calc.) 4.61 g/cm3 for Z = 3. The mineral is nonpleochroic, uniaxial negative, ω 1.763(5), ε 1.750(5). A single-crystal X-ray refinement of the structure (R = 0.078) showed the mineral to be rhombohedral, space group R3m, a 7.225(4), c 17.03(2) Å, and isostructural with corkite. The strongest lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 5.85(90)(101), 3.59(40)(110), 3.038(100)(113) and 2.271(40)(107). Within the crystals, in addition to gallobeudantite, are zones containing Ga-rich beudantite and hidalgoite, and the unnamed Ga analogues of segnitite, corkite, kintoreite, and arsenocrandallite. The last contains up to 12.7 wt.% GeO2, which is about 75% of the Ge substitution possible if the formula is assumed to be Ca(Ga,Al,Fe)2Ge4+(AsO4)2(OH) 6. The new name gallobeudantite alludes to the predominance of Ga in the position occupied by Fe3+ in beudantite-type minerals.
Jambor, JL; Owens, DR; Grice, JD; Feinglos, MN
Volume / Issue
Start / End Page