Gottlobite, CaMg(VO4,AsO4)(OH), a new mineral from Friedrichroda, Thuringia, Germany

Gottlobite is a new member of the adelite group. The mineral was found on t he dump of the long abandoned Glucksstern mine at the Gottlob hill, Friedri chroda, Thuringia (Thuringen), Germany. Gottlobite occurs as orange to oran ge-brown crystals and isometric grains up to 0.5 mm in size. The electron m icroprobe analysis gave (wt %, average of 19 points) CaO 24.98, SrO 0.92, M gO 17.54, MnO 1.50, CuO 1.44, V2O5 27.47, As2O5 20.32 and H2O (from thermog ravimetric analysis) 5.4, total 99.57. The empirical formula is (Ca0.93Sr0. 03) (Mg0.91Mn0.04Cu0.04) (V0.63As0.37)O4O1.08H1.26 (based on 1 V+As), and t he simplified formula is CaMg(VO4,AsO4)(OH) or CaMg(VO4)(OH) for the end-me mber composition. Gottlobite forms a solid solution with adelite. The miner al is orthorhombic, space group P2(1)2(1)2(1) with a = 7.501(4), b = 9.010( 7), c = 5.941(4) Angstrom, and V = 401.5(3) Angstrom (3), Z = 4. Gottlobite appears to be biaxial negative with the refractive indices alpha= 1.797(4) , beta between 1.805 and 1.815, gamma = 1.828(5). The crystal structure of gottlobite has been refined to R(F) = 0.0446 and wR(F-2)= 0.0852.