Vergasovaite Cu₃O[(Mo,S)O₄][SO₄], a new copper-oxy-molybdate-sulfate from Kamchatka

Vergasovaite occurs on encrustations of sulfates in fumaroles in the Northern part of the central fumarole field of cone II of the Northern Break of the Large Tolbachik Fissure Eruption (LTFE) on the Kamchatka peninsula. It is associated with chalcocyanite, dolerophanite, euchlorine, fedotovite, tenorite, Cu-bearing anglesite and native gold. Vergasovaite has an ideal formula Cu₃O[(Mo,S)O₄][SO₄]. Its space group is Pnma with a = 7.420(3), b = 6.741(2), c = 13.548(5) Å, V = 677.6(2) ų, and Z = 4. The five strongest lines d(calc) [Å] (I(calc), hkl) in the X-ray powder pattern are: 3.096 (100, 104); 3.377 (69, 020); 2.998 (56,121); 2.498 (54, 220); and 3.580 (37, 201). The olive-green mineral is transparent and distinctly pleochroic from olive-green to a yellowish to brownish-green. Microprobe analyses revealed a partial substitution of Mo by S and minor V, leading to the empirical formula (Cu(2.82(7)),Zn(0.10(7)), Pb(0.01(1)))(Σ = 2.92(9))O[(Mo(0.79(7)),S(0.20(5)),V(0.04(3)))(Σ = 1.04(3)O₄][SO₄]. IR spectroscopy showed vergasovaite to be free of H₂O and OH thus the mineral is a fully oxidized mixed copper-oxy-molybdate-sulfate. Vergasovaite is isostructural with synthetic Cu₃O[MoO₄]₂.