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The new mineral tsumgallite is a gallium oxide hydroxide, has the ideal chemical formular GaO(OH), is orthorhombic, space group Pbnm, with a = 4.512(5) A, b = 9.772(8) A, c = 2.967(4) A, cell volume 130.8(2) A 3 , Z = 4, from powder data. Cell parameter refined from powder data with the structure of α-gallium oxide deuteriohydroxide give a = 4.517 A, b = 9.760 A, c = 2.964 A, volume 130.7 A 3 . Tsumgallite is isostructural to goethite and diaspore. The strongest reflections in the X-ray powder diffraction data are as follows: (d m e a s . (A),I,(hkl)): 4.089(100)(110), 2.404(100)(111), 2.632(33)(130), 1.690(26)(221) and 2.530(22) (021). Tsumgallite was found at the Tsumeb mine, Tsumeb, Namibia. It forms tiny mica-like aggregates less than 1 mm across. Individual thin, platy crystals do not exceed 40 μm in size. The colour is a pale greenish yellow to beige. Tsumgallite is associated with of sohngeite and zincian siderite in vugs of a tennantite-germanite ore. Chemical analyses by electron microprobe gave Ga 2 O 3 78.13, Fe 2 O 3 3.99, GeO 2 4.01, ZnO 0.78, SiO 2 1.07, H 2 O ( i d e a l ) 8.77, sum 96,75 weight %, where the amount of water was taken from the ideal composition. The resulting empirical formular calculated on the basis of 2 anions is (Ga 0 . 8 6 , Fe 3 + 0.05, Ge 0 . 0 4 , Si 0 . 0 2 , Zn 0 . 0 1 ) Σ 0 . 9 8 O(OH) 1 . 0 1 . The mineral was named for the type locality and its chemical composition. Tsumgallite has been approved by the I.M.A. Commission on New Minerals and Mineral Names. |
