Luboržákite, Mn2AsSbS5, a new member of pavonite homologous series from Vorontsovskoe gold deposit, Northern Urals, Russia

Anatoly V. Kasatkin, Emil Makovicky, Jakub Plášil, Radek Škoda, Atali A. Agakhanov, Sergey Y. Stepanov, Roman S. Palamarchuk
2020 Mineralogical magazine  
Luboržákite, ideally Mn 2 AsSbS 5 , is a new mineral from the Vorontsovskoe gold deposit, Northern Urals, Russia. It forms long-prismatic crystals up to 70 x 20 μm and anhedral grains of the same size embedded in the matrix of Mn-bearing dolomite and Mn-bearing calcite. Associated minerals include pyrite, orpiment, realgar, stibnite, aktashite, alabandite, boscardinite, chabournéite, coloradoite, clerite, écrinsite, gold, routhierite, sphalerite, twinnite etc. Luboržákite is black, opaque with
more » ... etallic lustre and a black streak. It is brittle and has an uneven fracture. No cleavage and parting have been observed. Mohs hardness is 4-4½. D calc = 4.181 g·cm -3 . In reflected light, luboržákite is tin-white, weakly anisotropic with rotation tints varying from dark grey to grey. The chemical composition of luboržákite is (wt.%; electron microprobe, WDS mode): Mn 21.23, Cu 0.29, Ag 0.56, Pb 1.90, As 15.25, Sb 27.03, S 33.23, total 99.49. The empirical formula based on the sum of all atoms = 9 pfu is Mn 1.86 Pb 0.04 Ag 0.03 Cu 0.02 As 0.98 Sb 1.07 S 5.00 . The new mineral is monoclinic, space group C2/m with a = 12.5077(6), b = 3.8034(2), c = 16.0517(8) Å, β = 94.190(4), V = 761.57(6) Å 3 and Z = 4. The crystal structure of luboržákite was solved from the single-crystal X-ray diffraction data to R = 0.0383 for 712 observed reflections with I > 3σ(I). Luboržákite is a new member of the heterochemical isostructural series of 'unit-cell twinned' structures, named the pavonite series. The new mineral honors Lubor Žák, a prominent Czech crystallographer and the professor of the Charles University in Prague (Czech Republic).
doi:10.1180/mgm.2020.48 fatcat:xavp26pztvdrfb5liwmlsgzixu