Juanitaite, a new mineral from Gold Hill, Utah

Abstract

Juanitaite, (Cu,Ca,Fe)_(10)Bi(AsO_4)_4(OH)_(11)·2H_2O, is a new mineral from the Gold Hill mine, Tooele Co., Utah, USA The name is for Juanita Curtis who found the mineral. Juanitaite occurs as square crystal plates with rounded corners in sheaf-like subparallel aggregates and rosettes associated with conichalcite and mixite scattered over fracture surfaces on limonitic matrix. The mineral formed from oxidation of tennantite in quartz veins. Juanitaite is olive green to grass green with a pale greenish-yellow steak and resinous to dull luster. It is translucent and non-fluorescent. Crystals are tabular on {001} and also exhibit the forms: {110} and {310}. Twinning was not observed. Plates are flexible, but not elastic. Cleavage is perfect on {001} and {110} and good on {100}. Fracture was not observed. The specific gravity measured by sink-float in Clerici solution is 3.61(5) g/cm^3. The calculated density is 3.56 g/cm^3. Crystals are uniaxial (-), ω 1.785(5), є 1.705(5) (white light), but subparallel aggregates yield an anomalous biaxial figure (2V ≅ 20°). No dispersion was observed. Pleochroism: O = olive brown, E = olive green. Juanitaite is tetragonal, space group P4_2/nnm, ɑ = 9.961(3), c = 29.19(2) Å, V = 2896(2) Å^3, Z = 4. Electron microprobe analyses provided: CaO 8.64, FeO 2.32, CuO 35.97, Bi_2O_3 14.82, As_2O_5 29.35, H_2O 8.90 (by difference), total 100.00 wt%. H2O was confirmed by infrared spectroscopy. Juanitaite has a close chemical relationship with mixite, Cu_6Bi(AsO_4)_3(OH)_6·3H_2O. The six strongest powder diffraction lines are [d(Å)(I)(hkl)] 14.6(100)(002), 7.04(50)(110), 6.34(70)(112), 5.07(50)(114), 3.146(60)(310,303), 2.535(50)(228).

Additional details