• journal_title：The Canadian Mineralogist
• Contributor：Jiří Sejkora ; Jakub Plášil ; Petr Ondruš ; František Veselovský ; Ivana Císařová ; Jan Hloušek
• Publisher：Mineralogical Association of Canada
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.48.5.1157
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：48
• issue：5
• firstpage：1157
• section：Articles

Slavkovite, Cu₁₃(AsO₄)₆(AsO₃OH)₄·23H₂O, is a newly discovered supergene mineral from the Geschieber vein, Svornost mine at the Jáchymov (St. Joachimsthal) ore district, Czech Republic, commonly associated with lavendulan, geminite, lindackerite and ondrušite. It forms coatings of pale green rosettes up to 1 mm across or individual spherical aggregates up to 5 mm across. Individual acicular to lath-like crystals are up to 1 mm long and 0.05 mm thick, and are colorless with a greenish tint. Slavkovite is pale green, translucent (aggregates) to colorless with a greenish tint, transparent (crystals). It has a white streak and a vitreous luster, and does not fluoresce under both short- and long-wave ultraviolet light. The cleavage on {011} is perfect, and on {010}, it is good. The Mohs hardness is ~3.5–4; slavkovite is very brittle, with an irregular fracture. Its measured density, 3.05(1) g/cm³, is identical to the calculated one. Slavkovite is biaxial positive; the indices of refraction are α′ 1.591(2), β′ 1.620(2), γ′ 1.701(2), and the 2V (calc.) is approximately 64°. It is moderately pleochroic (X light gray to colorless, Y very light greenish gray, Z light green). Slavkovite is triclinic, space group P1̅, a 6.408(3), b 14.491(5), c 16.505(8) Å, α 102.87(3), β 101.32(5), γ 97.13(3)°, V 1442(1) ų, Z = 1, a:b:c = 0.4422:1:1.1390. The strongest eight lines in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are as follows: 15.70(3)(001), 11.98(100)(01̅1), 6.992(3)(02̅1, 020), 5.992(6)(02̅2), 3.448(5) (040), 2.967(5)(03̅5), 2.4069(4)(15̅4), 2.4002(4)(115, 1̅35, 04̅6, 06̅2). The chemical analyses made with an electron microprobe yielded FeO 0.12, CuO 39.93, Al₂O₃ 0.13, As₂O₅ 44.71, H₂O 17.31, total 102.20 wt.%. The resulting empirical formula on the basis of 63(O, OH, H₂O) anions is (Cu_12.96Al_0.07Fe_0.04)_∑13.07(AsO₄)_6.11 (AsO₃OH)_3.93·22.83H₂O. The ideal end-member formula, Cu₁₃(AsO₄)₆(AsO₃OH)₄·23 H₂O, requires CuO 39.26, As₂O₅ 43.36, H₂O 17.10, total 100.00 wt. %. The crystal structure of slavkovite has been solved by direct method and refined to a final R_obs of 4.37% on the basis of 6613 observed reflections collected on a single-crystal diffractometer with MoKα X-radiation. The crystal structure is based upon sheets consisting of copper polyhedra linked by arsenate and hydrogen arsenate tetrahedra. The sheets are linked by bridging Cu6–Φ polyhedra. In the asymmetric unit of the slavkovite unit-cell, seven symmetrically independent Cu²⁺ atoms, five As⁵⁺ atoms and 34 O atoms were found. Two of the oxygen atoms belong to OH⁻ groups and fourteen to H₂O molecules. Slavkovite possesses a unique crystal structure that has not been found in any mineral or synthetic compound before. It was named after its first occurrence in the Krásno Sn–W ore district, near Horní Slavkov, Czech Republic. Selected data for slavkovite from this locality are also given.