Hlousekite, (Ni,Co)Cu4(AsO4)2(AsO3OH)2(H2O)9, a new member of the lindackerite supergroup from Jachymov, Czech Republic

Hlous. ekite, (Ni,Co)Cu-4(AsO4)(2)(AsO3OH)(2)(H2O)(9), is a new supergene arsenate mineral from the Geister vein (Rovnost mine), Jachymov (St Joachimsthal), Western Bohemia, Czech Republic. It was found along with veselovskyite, pradetite, lavendulan, arsenolite, babanekite and gypsum on the surface of strongly altered ore fragments containing dominant tennantite and chalcopyrite. Hlous. ekite forms thin, lath-like crystals, locally elongated reaching up to 3 mm across. It is transparent, has a pale green colour with vitreous lustre, has a greyish-white streak and it is very brittle with an uneven fracture. It does not fluoresce under shortwave or longwave ultraviolet radiation. Cleavage on {010} is perfect; the Mohs hardness is 2-3. The calculated density is 3.295 g cm(-3). Hlous. ekite is optically biaxial with alpha' = 1.653(2) and gamma' = 1.73. The estimated optical orientation is gamma' vs. elongation (c) = 14(1)degrees. In larger grains it is weakly to moderately pleochroic (alpha = colourless, gamma = pale green to green). Hlousekite is triclinic, space group P (1) over bar, a = 6.4010(6), b = 8.0041(6), c = 10.3969(14) angstrom, alpha = 85.824(8), beta = 79.873(9), gamma = 84.655(7)degrees and V = 521.23(10) angstrom(3), with Z = 1, a:b:c = 0.800: 1: 1.299. The eight strongest lines in the powder X-ray diffraction (XRD) pattern [ d in angstrom (I)(hkl)] are 10.211(100)(001), 7.974(9)(010), 3.984(6)(020), 3.656(5)(1 (1) over bar2), 3.631(5)(0 (2) over bar1), 3.241(5)(022), 3.145(5)(200) and 3.006(5)(210). Chemical analysis by electron microprobe yielded MgO 0.20, FeO 0.10, NiO 5.79, CoO 1.80, CuO 29.53, ZnO 0.66, Al2O3 0.14, P2O5 0.11, As2O5 45.01, H2O 17.71 (calc.), for a total of 101.05 wt.%. The resulting empirical formula, calculated by stoichiometry (9H(2)O + 2OH), obtained from the crystal structure, is (Ni0.79Co0.25)(Sigma 1.04)(Cu3.78Zn0.08Mg0.05Al0.03Fe0.01)(Sigma 3.95) (AsO4)(1. 98)(PO4)(0.02)(AsO3OH)(2.00)(H2O)(9.00). The ideal endmember formula, NiCu4(AsO4)(2)(AsO3OH)(2)(H2O)(9.00), requires NiO 7.23, CuO 30.81, As2O5 44.51, H2O 17.45, total 100.00 wt.%. The crystal structure of hlous. ekite was solved by charge flipping from single-crystal XRD data and refined to R-1 = 0.0599 for 1441 reflections with [I-obs > 3 sigma(I)]. Hlousekite is a new member of the lindackerite group (also including lindackerite, pradetite and veselovskyite) of the lindackerite supergroup. The ondrusite group of the lindackerite supergroup includes ondrus. ite, chudobaite, geigerite and klajite. The establishment of these two groups reflects the difference between the crystal structures of their members, mainly in the coordination environment of the Me cations.