• journal_title：Mineralogical Magazine
• Contributor：A. R. Kampf ; S. J. Mills ; R. M. Housley ; G. R. Rossman ; B. P. Nash ; M. Dini ; R. A. Jenkins
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2013-08-01
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2013.077.6.08
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：77
• issue：6
• firstpage：2811
• section：CNMNC Newsletter 16

Joteite (IMA2012-091), Ca₂CuAl[AsO₄][AsO₃(OH)]₂(OH)₂·5H₂O, is a new mineral from the Jote mine, Tierra Amarilla, Copiapó Province, Atacama, Chile. The mineral is a late-stage, low-temperature, secondary mineral occurring with conichalcite, mansfieldite, pharmacoalumite, pharmacosiderite and scorodite in narrow seams and vughs in the oxidized upper portion of a hydrothermal sulfide vein hosted by volcanoclastic rocks. Crystals occur as sky-blue to greenish-blue thin blades, flattened and twinned on {001}, up to ~300 μm in length, and exhibiting the forms {001}, {010}, {11İ0}, {21İ0} and {111}. The blades are commonly intergrown in wheat-sheaf-like bundles, less commonly in sprays, and sometimes aggregated as dense crusts and cavity linings. The mineral is transparent and has a very pale blue streak and vitreous lustre. The Mohs hardness is estimated at 2 to 3, the tenacity is brittle, and the fracture is curved. It has one perfect cleavage on {001}. The calculated density based on the empirical formula is 3.056 g/cm³. It is optically biaxial (–) with α = 1.634(1), β = 1.644(1), γ = 1.651(1) (white light), 2V_meas = 78(2)° and 2V_calc = 79.4°. The mineral exhibits weak dispersion, r < v. The optical orientation is X ≈ c*; Y ≈ b*. The pleochroism is Z (greenish blue) > Y (pale greenish blue) > X (colourless). The normalized electron-microprobe analyses (average of 5) provided: CaO 15.70, CuO 11.22, Al₂O₃ 8.32, As₂O₅ 46.62, H₂O 18.14 (structure), total 100 wt.%. The empirical formula (based on 19 O a.p.f.u.) is: Ca_1.98Cu_1.00Al_1.15As_2.87H_14.24O₁₉. The mineral is slowly soluble in cold, concentrated HCl. Joteite is triclinic, P1İ, with the cell parameters: a = 6.0530(2), b = 10.2329(3), c = 12.9112(4) Å, α = 87.572(2), β = 78.480(2), γ = 78.697(2)°, V = 768.40(4) ų and Z = 2. The eight strongest lines in the X-ray powder diffraction pattern are [d_obs Å(I)(hkl)]: 12.76(100)(001), 5.009(23)(020), 4.206(26)(120,003,121), 3.92(24)(022,02İ2,1İ02), 3.40(25)(1İ13), 3.233(19)(031,023,123,02İ3), 2.97(132,201) and 2.91(15)(1İ22,1İ13). In the structure of joteite (R₁ = 7.72% for 6003 F_o > 4σF), AsO₄ and AsO₃(OH) tetrahedra, AlO₆ octahedra and Cu²⁺O₅ square pyramids share corners to form sheets parallel to {001}. In addition, 7- and 8-coordinate Ca polyhedra link to the periphery of the sheets yielding thick slabs. Between the slabs are unconnected AsO₃(OH) tetrahedra, which link the slabs only via hydrogen bonding. The Raman spectrum shows features consistent with OH and/or H₂O in multiple structural environments. The region between the slabs may host excess Al in place of some As.