Abramovite, Pb2SnInBiS7, a new mineral species from fumaroles of the Kudryavy volcano, Kurile Islands, Russia

Abramovite, a new mineral species, has been found as fumarole crust on the Kudryavy volcano, Iturup Island, Kuriles, Russia. The mineral is associated with pyrrhotite, pyrite, wurtzite, galena, halite, sylvite, and anhydrite. Abramovite occurs as tiny elongated lamellar crystals up to 1 mm long and 0.2 mm wide (average 300 × 50 μ m), which make up chaotic intergrowths in the narrow zone of fumarole crust formed at ∼600°C. Most crystals are slightly striated along the elongation. The new mineral is silver gray, with a metallic luster and black streak. Under reflected light, abramovite is white with a yellowish gray hue. It has weak bireflectance; anisotropy is distinct without color effects. The chemical composition (electron microprobe) is as follows, wt %: 20.66 S, 0.98 Se, 0.01 Cu, 0.03 Cd, 11.40 In, 12.11 Sn, 37.11 Pb, 17.30 Bi; the total is 99.60. The empirical formula calculated on the basis of 12 atoms is Pb1.92Sn1.09In1.06Bi0.89(S6.90Se0.13)7.03. The simplified formula is Pb2SnInBiS7. The strongest eight lines in the X-ray powder pattern [d, A (I)(hkl)] are 5.90(36)(100), 3.90(100)(111), 3.84(71)(112), 3.166(26)(114), 2.921(33)(115), 2.902(16)(200), 2.329(15)(214), 2.186(18)(125). The selected area electron diffraction (SAED) patterns of abramovite are quite similar to those of the homologous cylindrite series minerals. The new mineral is characterized by noncommensurate structure composed of regularly alternated pseudotetragonal and pseudohexagonal sheets. The structure parameters determined from the SAED patterns and X-ray powder diffraction data for pseudotetragonal subcell are: a = 23.4(3), b = 5.77(2), c = 5.83(1) A, α = 89.1(5) °, β = 89.9(7)°, γ = 91.5(7)°, V = 790(8) A3; for pseudohexagonal subcell: a = 23.6(3), b = 3.6(1), c = 6.2(1) A, α = 91(2)°, β = 92(1)°, γ = 90(2)°, V = 532(10) A3. Abramovite is triclinic, space group P(1). The new mineral is named in honor of Russian mineralogist Dmitry Abramov. The type material of abramovite has been deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.