Raisaite, CuMg[Te6+O4 (OH)2]· 6H2O, a new mineral from Chukotka, Russia
Pekov, Igor V.; Vlasov, Evgeniy A.; Zubkova, Natalia V.; Yapaskurt, Vasiliy O.; Chukanov, Nikita V.; Belakovskiy, Dmitry I.; Lykova, Inna S.; Apletalin, Andrey V.; Zolotarev, Andrey A.; Pushcharovsky, Dmitryy.
European Journal of Mineralogy Volume 28 Number 2 (2016), p. 459 - 466
published: May 1, 2016
Raisaite, CuMg[Te6+ O4 (OH)2] ·6H2 O, is a new mineral found at the Sentyabr'skoe deposit, Ilirney ore district, Western Chukotka, North-Eastern Region, Russia. It is associated with gypsum, malachite, azurite, cerussite, anglesite, brochantite, linarite, posnjakite, chlorargyrite, acanthite, gold, brucite, goethite, coronadite, paratellurite, and xocomecatlite in the oxidation zone of quartz veins with calcite, dolomite, ankerite, muscovite, pyrite, chalcopyrite, galena, sphalerite, hessite, petzite, altaite, primary acanthite and gold, etc. Raisaite occurs as prismatic crystals (up to 0.1 x 0.6 mm), as groups or crusts (up to 0.4 x 0.6 mm) and as dense roundish clusters (up to 0.2 mm in diameter) forming botryoidal aggregates (up to 1 mm across). Raisaite is transparent, light blue to bright sky blue, with a vitreous lustre. Its Mohs' hardness is ca. 2. Cleavage is imperfect, probably on (100), the fracture is uneven. D meas = 2.82(1), D calc = 2.828 g cm3. Raisaite is optically biaxial (+), α = 1.626(3), β = 1.642(5), γ = 1.665(3) and 2 V meas = 80(10)° . The IR spectrum is reported. The chemical composition (average of 7 analyses, H2 O by difference) is: MgO 10.68, CuO 18.09, SO3 0.44, TeO3 41.19, H2 Ocalc 29.60, total 100.00 wt%. The empirical formula calculated on the basis of 12 O apfu is: Cu0.96 Mg1.11 Te0.99 S0.02 O4.20 (OH)1.80 6.00H2 O. Raisaite is monoclinic, C 2/ c , a = 9.9078(2), b = 10.1325(3), c = 9.8375(2) Å, β = 91.839(2)Å, V = 987.09(4)Å 3 and Z = 4. The strongest reflections of the powder X-ray diffraction pattern [d, Å (I)(hkl)] are: 7.088(100)(110), 5.815(35)(–111), 5.690(23)(111), 4.949(91)(200, 002), 4.507(50)(021), 3.533(17)(–202, 022), 3.358(17)(–221), 3.310(21)(221) and 2.694(29)(–132). The crystal structure (solved from single-crystal X-ray diffraction data, R = 0.0186) is unique. It is based on heteropolyhedral zig-zag chains built by alternating edge-sharing Te6+O4 (OH)2 and CuO4 (H2 O)2 octahedra. Mg(H2 O)6 octahedra are connected with the chains from two sides via common O vertices. Adjacent chains are bound by H-bonding forming ''layers'' which are connected with each other by a system of H-bonds. The mineral is named in honour of the Russian mineralogist Raisa A. Vinogradova (born 1935), Moscow State University. Both the new mineral and its name have been approved by the IMA CNMNC (IMA2014-046).