Ondrušite, CaCu4(AsO4)2(AsO3OH)2.10H2O, a new mineral species from the Jáchymov ore district, Czech Republic:description and crystal-structure determination
Abstrakt
Ondrusite, CaCu4(AsO4)2(AsO3OH)2 . 10H2O, is a new supergene mineral species from the Geister vein (Rovnost mine) and the Geschieber vein (Svornost mine), at the Jachymov (St. Joachimsthal) ore district, Czech Republic.
It is commonly associated with lindackerite, geminite, lavendulan, slavkovite, strashimirite, olivenite, picropharmacolite and kottigite. It forms white, whitish green, grey-green or apple-green crystalline crusts or aggregates composed of fine platy or lath-shaped translucent crystals up to 2 mm in size, on fissures of partly weathered mineralized quartz veins.
It has a white to greyish white streak with a greenish tint, and a vitreous luster; it does not fluoresce under both short- and long-wave ultraviolet light. Cleavage on {001} is perfect, the Mohs hardness is similar to 2-3, and the mineral is very brittle with an irregular fracture.
Ondrusite is triclinic, space group P-1, a 6.432(1), b 7.986(1), c 10.827(1) angstrom, alpha 85.75(1), beta 81.25(1), gamma 85.04(1)degrees, V 546.6(1) angstrom3, Z = 1. The chemical analyses by electron microprobe and the thermal analysis for H2O yielded MgO 0.42, CaO 5.27, NiO 0.03, CoO 0.08.
CuO 29.90, PbO 0.16, P2O5 0.33, As2O5 44.92, H2O 19.40, for a total of 100.51 wt.%. The crystal structure of ondrusite was solved by direct method and refined to a R1 index of 9.80% based on all 2888 reflections collected on a single-crystal diffractometer with MoKalpha X-radiation.
The crystal structure consists of CuO6-AsO4-AsO3OH chains two polyhedra thick that form sheets connected through the bridging CaO6 octahedra. In the sheet-to-sheet bonding, CaO6 octahedra and AsO4 groups are involved, whereas the AsO3OH groups bond the CuO6 polyhedra only.
One other H2O group is located between the sheets.