| Description |
Babanekite, Cu-3(AsO4)(2) center dot 8H(2)O, a new member of the vivianite group was found in material originating from the Geister vein, Rovnost mine, Jachymov, Western Bohemia, Czech Republic. It occurs as a supergene alteration mineral in association with members of the lindackerite supergroup (veselovskyite, hlousekite, pradetite and lindackerite), lavendulan, gypsum and an X-ray amorphous Cu-Al-Si-O-H phase. Crystals of babanekite are pinkish to peach-colored, elongated, prismatic and up to 2 mm in length. They exhibit the forms {010}, {100}, {110}, {101} and less frequently also {001}. Crystals are transparent to translucent with a vitreous luster. The mineral has a light pinkish streak. Estimated Mohs hardness is between 1.5 and 2. The cleavage is perfect on {010}. The calculated density is 3.192 g/cm(3). Electron-microprobe analysis yielded CoO 8.89, NiO 4.06, CuO 15.31, ZnO 10.87, P2O5 0.16, As2O5 39.79, SO3 0.13, H2O 24.78 (calc.), total 103.99 wt.% giving the empirical formula (Cu1.12Zn0.78Co0.69Ni0.32)(Sigma 2.91)[(AsO4)(2.01)(PO4)(0.01)(SO4)(0.01)](Sigma 2.03) center dot 8H(2)O based on 16 O apfu. The ideal end-member formula of babanekite is Cu-3(AsO4)(2) center dot 8H(2)O, which requires CuO 38.95, As2O5 37.52, H2O 23.53, total 100.00 wt.%. Babanekite is monoclinic, C2/m, with a = 10.1729(3), b = 13.5088(4), c = 4.7496(1) angstrom, beta = 105.399(2)degrees, V = 629.28(3) angstrom(3) and Z = 2. The eight strongest X-ray powder diffraction lines are [d(obs) angstrom(I)(hkl)]: 7.936(11)(110), 6.743(100)(020), 3.231(14)(13-1), 2.715(11)(041), 2.3331(10)(15-1), 2.0819(5)(350), 1.6862(16)(080) and 1.6107(4)(55-1). The crystal structure of babanekite, refined to R-1 = 2.18 % for 864 unique observed reflections, confirmed that the atomic arrangement is similar to other members of the vivianite group of minerals. The mineral is named for Ing. Frantisek Babanek (1836-1910), Czech mining and geological expert, who worked in the Jachymov and Pribram mines.
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