Karpenkoite, Co3(V2O7)(OH)2•2H2O, a cobalt analogue of martyite from the Little Eva mine, Grand County, Utah, USA

Karpenkoite (IMA 2014-092), ideally Co-3(V2O7)(OH)(2)center dot 2H(2)O, is a new divanadate mineral species, the cobalt analogue of martyite, found at the Little Eva mine, Grand County, Utah, USA. It occurs on sandstone matrix in close association with martyite, quartz, gypsum, baryte, roscoelite and an unidentified Al vanadate. Karpenkoite is a secondary mineral formed during the post-mining oxidation of corvusite and montroseite in a moist environment at ambient temperatures. The new mineral occurs as lamellar crystals, coarsely hexagonal or irregular in shape, typically curved. The crystals form rose-like clusters or globular aggregates up to 0.2 mm across. Karpenkoite is orange with pale yellow-orange streak. It is transparent with a vitreous luster. The mineral is brittle, with laminated fracture and perfect cleavage on {001}. The calculated density is 3.415 g cm(-3). The mineral is optically uniaxial (+), with omega = 1.827(8) and epsilon = 1.843(8). The chemical composition of karpenkoite (wt. %, electron-microprobe data) is: MgO 0.05, CaO 0.26, MnO 1.39, CoO 33.22, NiO 2.02, CuO 0.28, ZnO 12.66, V(2)O(5)38.70, H2O (calc.) 11.61, total 100.19. The empirical formula, calculated on the basis of 11 O apfu, is (Co2.06Zn0.72Ni0.13Mn0.09Ca0.02Cu0.02Mg0.01)(Sigma 3.05)V1.98O7(OH)(2)center dot 2H(2)O. The Raman spectrum demonstrates symmetric stretching and bending vibrations of V5+O3 units and the O-H stretching and bending vibrations of the H2O molecules. The new mineral is trigonal, the most probable space group is P (3) over bar m1 (by analogy with its Zn analogue martyite), a = 6.016(4), c = 7.234(6)angstrom, V = 226.7(2)angstrom(3) and Z = 1. The strongest powder X-ray diffraction lines are [d(obs),angstrom(I)(hkl)]: 7.15(100)(001), 5.19(18)(010), 4.20(25)(101,011), 3.59(21)(002), 2.95(54)(012,102), 2.77(21)(111), 2.60(36)(200), and 2.44(33)(201,021). The new mineral is named in honor of the Russian mineralogist Vladimir Yu. Karpenko (b. 1965), an expert on the mineralogy of vanadium.