Eurekadumpite, (Cu,Zn)16(TeO3)2(AsO4)3Cl(OH)18·7H2O, a new supergene mineral species

Abstract

A new mineral eurekadumpite found at the Centennial Eureka Mine in the Tintic district of Juab County in Utah in the United States occurs in the oxidation zone along with quartz, macalpineite, malachite, Zn-bearing olivenite, goethite, and Mn oxides. Eurekadumpite forms spherulites or rosettes up to 1 mm in size and their clusters and crusts up to 1.5 cm2 in cavities. Its individuals are divergent and extremely thin (up to 0.5 mm across and less than 1 μm thick) hexagonal or roundish leaflets. The mineral is deep blue-green or turquoise-colored. Its streaks are light turquoise-colored. Its luster is satiny in aggregates and pearly on individual flakes. Its cleavage is (010) perfect and micalike. Its flakes are flexible but inelastic. Its Mohs hardness is 2.5–3.0, and D(meas) = 3.76(2) and D(calc) = 3.826 g/cm3. The mineral is optically biaxial negative, and α = 1.69(1), β ∼ γ = 1.775(5), and 2Vmeas = 10(5)°. Its pleochroism is strong: Y = Z = deep blue-green, and X = light turquoise-colored. Its orientation is X = b. The wavenumbers of the bands in the IR spectrum (cm−1; the strong lines are underlined, and w denotes the weak bands) are 3400, 2990, 1980w, 1628, 1373w, 1077, 1010, 860, 825, 803, 721w, 668, 622, 528, 461. The IR spectrum shows the occurrence of the tellurite (Te4+,O3)2− and arsenate (As5+,O4)3− anionic groups and H2O molecules; Cu and Zn cations are combined with OH− groups. The chemical composition of eurekadumpite is as follows (wt %, average of 14 electron-microprobe analyses; H2O determined using the Alimarin method): 0.04 FeO, 36.07 CuO, 20.92 ZnO, 14.02 TeO2, 14.97 As2O5, 1.45 Cl, 13.1 H2O, O = Cl2 −0.33, total 100.24. The empirical formula based on 2 Te atoms is (Cu10.32Zn5.85Fe0.01)Σ16.18(TeO3)2(AsO4)2.97[Cl0.93(OH)0.07]Σ1(OH)18.45 · 7.29H2O. The idealized formula is (Cu,Zn)16(TeO3)2(AsO4)3Cl(OH)18 · 7H2O. Eurekadumpite is monoclinic (pseudohexagonal), and the most probable space groups are P2/m, P2, or Pm. The unit-cell parameters refined from the powder X-ray data are as follows: a = 8.28(3), b = 18.97(2), c = 7.38(2) A, β = 121.3(6)°, V = 990(6) A3, and Z = 1. The strongest reflections of the X-ray powder pattern (d, A (I) [hkl]) are as follows: 18.92(100) [010], 9.45(19) [020], 4.111(13) [\(\bar 2\) 01], 3.777(24) [050, \(\bar 2\) 21, 041], 2.692(15) [\(\bar 3\) 11, 151, \(\bar 3\) 02], 2.524(41)[170, \(\bar 2\) 52, \(\bar 1\) 71], 1.558(22) [\(\bar 4\) 82, \(\bar 3\) .10.1, 024]. The name of the mineral means, firstly, that it was found in specimens from dumps of the Centennial Eureka Mine. In addition, it could mean found in a dump (the Greek word eureka means I have found it). There is an allusion to the great role that dumps of abandoned mines have played in the discovery of new minerals. Type specimens are deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow, at the Smithsonian National Museum of Natural History in Washington, and at the American Museum of Natural History in New York.