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) Å, b = 9.772(8) Å, c = 2.967(4) Å, cell volume 130.8(2) Å3, Z = 4, from powder data. Cell parameter refined from powder data with the structure of α-gallium oxide deuteriohydroxide give a = 4.517 Å, b = 9.760 Å, c = 2.964 Å, volume 130.7 Å3. Tsumgallite is isostructural to goethite and diaspore. The strongest reflections in the X-ray powder diffraction data are as follows: (dmeas.(Å , 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 söhngeite and zincian siderite in vugs of a tennantite-germanite ore. Chemical analyses by electron microprobe gave Ga2O3 78.13, Fe2O3 3.99, GeO2 4.01, ZnO 0.78, SiO2 1.07, H2O(ideal) 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 (Ga0.86, Fe3+0.05, Ge0.04, Si0.02, Zn0.01)∑0.98 O(OH)1.01. 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.