Tsygankoite, Mn8Tl8Hg2(Sb21Pb2Tl)Σ24S48, a New Sulfosalt from the Vorontsovskoe Gold Deposit, Northern Urals, Russia

Tsygankoite, ideally Mn8Tl8Hg2(Sb21Pb2Tl)(Sigma 24)S-48, is a new sulfosalt discovered at the Vorontsovskoe gold deposit, Northern Urals, Russia. It occurs as lath-like elongated crystals up to 0.2 mm embedded in calcite-dolomite-clinochlore matrix. The associated minerals also include aktashite, alabandite, arsenopyrite, barite, cinnabar, fluorapatite, orpiment, pyrite, realgar, routhierite, sphalerite, tilasite, and titanite. The new mineral is non-fluorescent, black, and opaque with a metallic lustre and black streak. It is brittle with an uneven fracture and no obvious parting and cleavage. Its Vickers hardness (VHN10) is 144 kg/mm(2) (range 131-167 kg/mm(2)) and its calculated density is 5.450 g.cm(-3). In reflected light, tsygankoite is white; between crossed polars it is dark grey to black. It is strongly anisotropic: rotation tints vary from light grey to dark grey to black. Pleochroism and internal reflections are not observed. The chemical composition of tsygankoite (wt %, electron-microprobe data) is: Mn 6.29, Hg 5.42, Tl 26.05, Pb 5.84, As 3.39, Sb 30.89, S 21.87, total 99.75. The empirical formula, calculated on the basis of 90 atoms pfu, is: Mn8.06Tl8.00Hg1.90(Sb17.87As3.19Pb1.99Tl0.97)Sigma S-24.02(48.03). Tsygankoite is monoclinic, space group C2/m, a = 21.362(4) angstrom, b = 3.8579(10) angstrom, c = 27.135(4) angstrom, = 106.944(14)degrees, V = 2139.19(17) angstrom(3) and Z = 1. The five strongest diffraction peaks from X-ray powder pattern (listed as (d,angstrom(I)(hkl)) are: 3.587(100)(112), 3.353(70)(-114), 3.204(88)(405), 2.841(72)(-513), and 2.786(99)(-514). The crystal structure of tsygankoite was refined from single-crystal X-ray diffraction data to R = 0.0607 and consists of an alternation of two thick layer-like arrays, one based on PbS-archetype and the second on SnS-archetype. Tsygankoite has been approved by the IMA-CNMNC under the number 2017-088. It is named for Mikhail V. Tsyganko, a mineral collector from Severouralsk, Northern Urals, Russia, who collected the samples where the new mineral was discovered.