The new mineral genplesite, Ca3Sn(SO4)2(OH)6∙3H2O, the first natural tin sulfate, is found in cavities in massive chalcopyrite ore at the Oktyabr'skoe Cu-Ni-Pd-Pt deposit (Oktyabr'sky mine), Talnakh, Norilsk district, Siberia, Russia. It is a late-stage hydrothermal mineral associated with greenalite, chamosite, pectolite, ferroactinolite, calcite and fluorapatite. Genplesite occurs as equant, short prismatic or thick tabular hexagonal crystals up to 0.5 mm and crystal clusters up to 0.6 × 1.2 mm. The major crystal forms are {1 0 0} and {0 0 1} whereas {1 0 2} and {1 0 1} are minor. Genplesite is transparent, colourless, with vitreous lustre. It is brittle, the Mohs hardness is ca. 3. Cleavage is not observed, the fracture is conchoidal. Dmeas = 2.78(1), Dcalc = 2.773 g · cm−3. Genplesite is optically uniaxial (–), ω = 1.597(2), ε = 1.572(2). The IR spectrum is reported. The chemical composition (wt%, electron microprobe data, H2O calculated for 3 molecules per formula unit, pfu) is: CaO 28.67, Al2O3 0.11, GeO2 0.50, SnO2 24.20, SO3 27.25, H2Ocalc 18.34, total 99.07. The empirical formula calculated on the basis of 17 O apfu is: Ca3.01(Sn0.95Ge0.03Al0.01)Σ0.99S2.01O8(OH)6∙3H2O. Genplesite is hexagonal, P63/mmc, a = 8.5139(2), с = 11.1408(3) Å, V = 699.37(1) Å3 and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d, Å (I)(hkl)] are: 7.38(68)(100), 4.259(46)(110), 3.503(15)(201), 3.383(100)(112), 2.616(13)(203), 2.493(14)(212), 2.249(14)(302) and 2.130(17)(105, 220). Genplesite is a member of the fleischerite group. Its crystal structure was solved from single-crystal X-ray diffraction data (R = 0.016). The major building unit of the structure is a column consisting of isolated Sn4+(OH)6 octahedra and trimers of edge-sharing CaO2(OH)4(H2O)2 polyhedra. Adjacent columns are interconnected via H2O molecules and SO4 tetrahedra. Genplesite is named in honour of Gennadiy N. Plesin (b. 1963), a mine surveyor at the Oktyabr'sky mine and an amateur mineralogist who found the mineral.

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