New nickel-uranium-arsenic mineral species from the oxidation zone of the Belorechenskoye deposit, Northern Caucasus, Russia: II. Dymkovite, Ni(UO2)(2)(As3+O3)(2)center dot 7H(2)O, a seelite-related arsenite

作者：Pekov Igor V^*; Levitskiy Viktor V; Krivovichev Sergey V; Zolotarev Andrey A; Chukanov Nikita V; Bryzgalov Igor A; Zadov Aleksandr E

来源：European Journal of Mineralogy, 2012, 24(5): 923-930.

DOI：10.1127/0935-1221/2012/0024-2219

• dymkovite
• new mineral species
• arsenite
• seelite
• crystal structure
• oxidation zone
• Belorechenskoye deposit
• Adygea

A new arsenite mineral species dymkovite, ideally Ni(UO2)(2)(As3+O3)(2)center dot 7H(2)O (IMA no. 2010-087), was found at the Belorechenskoye deposit, Adygea Republic, Northern Caucasus, Russia. It is a supergene mineral associated with rauchite, annabergite, and goethite in cavities of a dolomite vein with primary uraninite (pitchblende), nickeline, and gersdorffite. Dymkovite forms long-prismatic, lath-shaped to acicular crystals (%26lt;= 0.5 mm long, %26lt;= 0.05 mm thick), which are elongated along [010]. They are combined in sprays or open-work, chaotic groups up to 1.5 mm across; crusts up to 2 x 2 mm(2) and up to 0.05-mm-thick also occur. Dymkovite crystals are transparent and bright yellow, whereas crusts are translucent and light yellow to light greenish-yellow. The luster is vitreous. The mineral is brittle, the Mohs%26apos; hardness is ca. 3. Cleavage was not observed. D-calc is 3.806 g cm(-3). Dymkovite is optically biaxial (-), alpha = 1.625(2), beta = 1.735(5), gamma = 1.745(3), 2V(meas) = 20(10)degrees, 2V(calc.) = 32 degrees. Dispersion is strong, r %26gt; v. Pleochroism is strong: X = very pale yellowish-green, Y approximate to Z = light greenish yellow. In the IR spectrum, bands of As3+O3 anions are strong, whereas bands of As5+O4 anions are very weak. The average chemical composition (electron microprobe) is (in wt%): MgO = 1.11, FeO = 0.24, NiO = 5.40, ZnO = 0.23, As2O3 = 19.57, P2O5 = 0.58, UO3 = 59.43, H2Ocalc = 13.44, total = 100.00. The empirical formula, calculated on the basis of 17 O apfu, is: (Ni0.69Mg0.26Fe0.03Zn0.03)(Sigma 1.01) U-1.97(As1.883+P0.08)(Sigma 1.96)O-9.94 center dot 7.06H(2)O. Dymkovite is monoclinic, space group C2/m, a = 17.99(3), b = 7.033(7), c = 6.633(9) angstrom, beta = 99.62(11)degrees, V = 827(3) angstrom(3), Z = 2. The crystal structure was refined from single-crystal X-ray diffraction data (R-1 = 0.063). The structure is based upon the [(UO2)(As3+O3)](-) sheets formed by chains of edge-sharing [UO7] pentagonal bipyramids and (As3+O3) triangular pyramids, which are linked through hydrogen bonds involving disordered [Ni(H2O)(6)](2+) octahedra and additional H2O molecules in the interlayer. The strongest lines of the powder X-ray pattern [d in angstrom (I)(hkl)] are: 8.93(100)(200), 4.463(34)(111, 400), 3.523(23)(020), 3.276(21)(220), 3.008(26)(11-2), 2.846(27)(112, 221, 31-2). Dymkovite is a Ni-dominant, almost arsenate-free analogue of seelite, Mg(UO2)(2)[(As3+O3)(1.4)(As5+O4)(0.6)]center dot 7H(2)O. The mineral is named in honor of the Russian mineralogist Yuriy Maksimovich Dymkov (b. 1926), a specialist in U mineralogy, the geology of U deposits, and problems of mineral formation, who was one of the first researchers of the U ores of the Belorechenskoye deposit.

• 出版日期2012-10