Goldquarryite, a new Cd-bearing phosphate mineral from the Gold Quarry mine, Eureka County, Nevada

Abstract

Goldquarryite, idealized formula CuCd2Al3(PO44F2(H2O)10(H2O 2, structure-derived formula (Cu0.70???0.30??1.00(Cd1.68Ca0.32??2.00Al3 (PO44F2(H2O)10[(H2O 1.60F0.40]??2.00, is triclinic, space group P1, with unit-cell parameters derived from crystal structure: a = 6.787(1), b = 9.082(2), c = 10.113(2) A??, ?? = 101.40(1)??, ?? = 104.27(1)??, ?? = 102.51(1)??, V = 568.7(3) A??3, a:b:c: = 0.7473:1:1.1135, Z = 1. The strongest seven reflections in the X-ray powder-diffraction pattern are [d(A??)(I)(hkl)]: 9.433(100)(001); 4.726(30)(002); 3.700(30)(022); 3.173(30b)(122, 113, 120, 003); 3.010(30)(122, 212); 2.896(30)(211); 2.820(50)(022). The mineral occurs on a single specimen collected from the 5,425-foot bench, Gold Quarry mine, Eureka County, Nevada, as isolated clusters of radiating sprays of crystals and as compact parallel crystal aggregates, which are both found on and between breccia fragments. Sprays and aggregates never exceed 3 mm in longest dimension and typically average about 0.5 mm in size. Goldquarryite is a late-stage supergene mineral associated with opal, carbonate-fluorapatite and hewettite, on a host rock composed principally of brecciated and hydrothermally rounded jasperoid fragments which have been lightly cemented by late-stage silicification. Individual euhedral crystals are acicular to bladed, elongate [100], with a length-to-width ratio of approximately 20:1; the maximum size is 1.5 mm but most crystals do not exceed 0.4 mm in length. Forms are {010}, {001} major and {100} very minor. The mineral is pleochroic; translucent (masses) to transparent (crystals); very pale blue to blue-gray (crystals) or blue (masses); with a white streak and a vitreous to glassy luster. Goldquarryite is brittle, lacks cleavage, has an irregular fracture, and is nonfluorescent; hardness (Mohs') is estimated at 3-4; measured density is 2.78(1) g/cm3 (sink-float techniques using methylene iodide-acetone mixtures), calculated density is 2.81 g/cm3 (for formula and unit-cell parameters derived from crystal structure). Optically, it is biaxial positive, ?? = 1.570, ?? = 1.573, ?? = 1.578; 2V (meas.) = ???30??, 2V (calc.) = 76??; dispersion r < v, strong. Average electron-microprobe analysis: K2O = 0.17, CuO = 5.33, CaO = 1.25, NiO = 0.23, ZnO = 0.05, CdO = 26.24, Al2O3 = 15.22, V2O3 = 0.05, P2O5 = 28.04, F = 3.63, H2O (calculated assuming stoichiometry) = [22.19], -O = F = -1.53, total = 100.87 weight %, corresponding to [(Cu0.66Ni0.03Zn0.01) ??0.70.