Belakovskiite, Na7(UO2)(SO4)4(SO3OH)(H2O)3, a new uranyl sulfate mineral from the Blue Lizard mine, San Juan County, Utah, USA

The new mineral belakovskiite (IMA2013-075), Na-7(UO2)(SO4)(4)(SO3OH)(H2O)(3), was found in the Blue Lizard mine, Red Canyon, White Canyon district, San Juan County, Utah, USA, where it occurs as a secondary alteration phase in association with blodite, ferrinatrite, krohnkite, meisserite and metavoltine. Crystals of belakovskiite are very pale yellowish-green hair-like fibres up to 2 mm long and usually no more than a few mu m in diameter. The fibres are elongated on [100] and slightly flattened on {021}. Crystals are transparent with a vitreous lustre. The mineral has a white streak and a probable Mohs hardness of similar to 2. Fibres are flexible and elastic, with brittle failure and irregular fracture. No cleavage was observed. The mineral is readily soluble in cold H2O. The calculated density is 2.953 g cm(-3). Optically, belakovskiite is biaxial (+) with alpha = 1.500(1), beta = 1.511(1) and gamma = 1.523(1) (measured in white light). The measured 2V is 87.1(6)degrees and the calculated 2V is 88 degrees. The mineral is non-pleochroic. The partially determined optical orientation is X approximate to a. Electron-microprobe analysis provided Na2O 21.67, UO3 30.48, SO3 40.86, H2O 6.45 (structure), total 99.46 wt.% yielding the empirical formula Na-6.83(U1.04O2)(SO4)(4)(S0.99O3OH)(H2O)(3) based on 25 O a.p.f.u. Belakovskiite is triclinic, P (1) over bar, with a = 5.4581(3), b = 11.3288(6), c = 18.4163(13) angstrom, alpha =104.786(7)degrees, beta = 90.092(6)degrees, gamma = 96.767(7)degrees, V = 1092.76(11) angstrom(3) and Z = 2. The eight strongest X-ray powder diffraction lines are [d(obs) angstrom(I)(hkl)]: 8.96(35)(002), 8.46(29)(011), 5.19(100)((1) over bar 01,101,(1) over bar 10), 4.66(58)(013,(1) over bar 02,(1) over bar(1) over bar0,110), 3.568(37)(120,023,005,0 (3) over bar3), 3.057(59)(0 (1) over bar6,1 (1) over bar5,(1) over bar 31), 2.930(27)(multiple) and 1.8320(29)(multiple). The structure, refined to R-1 = 5.39% for 3163 F-o > 4 sigma F reflections, contains [(UO2)(SO4)(4)(H2O)](6)- polyhedral clusters connected via an extensive network of Na-O bonds and H bonds involving eight Na sites, three other H2O sites and an SO3OH (hydrosulfate) group. The 3-D framework, thus defined, is unique among known uranyl sulfate structures. The mineral is named for Dmitry Ilych Belakovskiy, a prominent Russian mineralogist and Curator of the Fersman Mineralogical Museum.