Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Anatoly V. Kasatkin, Jakub Plášil, Igor V. Pekov, Dmitry I. Belakovskiy, Fabrizio Nestola, Jiří Čejka, Marina F. Vigasina, Federico Zorzi, Brent Thorne

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

Journal of Geosciences, volume 60 (2015), issue 4, 251 - 257

DOI: http://doi.org/10.3190/jgeosci.199

Karpenkoite (IMA 2014-092), ideally Co₃(V₂O₇)(OH)₂·2H₂O, 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 ω = 1.827(8) and ε = 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, V₂O₅ 38.70, H₂O (calc.) 11.61, total 100.19. The empirical formula, calculated on the basis of 11 O apfu, is (Co_2.06Zn_0.72Ni_0.13Mn_0.09Ca_0.02Cu_0.02Mg_0.01)_Σ3.05V_1.98O₇(OH)₂·2H₂O. 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 m1 (by analogy with its Zn analogue martyite), a = 6.016(4), c = 7.234(6) Å, V = 226.7(2) ų and Z = 1. The strongest powder X-ray diffraction lines are [d_obs,Å(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 in the mineralogy of vanadium.