Parnauite and goudeyite, two new copper arsenate minerals from the Majuba Hill Mine, Pershing County, Nevada

Parnauite and goudeyite were found with other secondary copper minerals in the middle adit level of the Majuba Hill Mine, Pershing County, Nevada.

Parnauite occurs as pale-blue fans and rosettes of lath-like crystals up to 1 mm in length, as green scales and crusts, and drusy surface coatings. A combination of electron microprobe analyses and microanalyses for H₂0 and C0₂ give the following composition: CuO 58.10, A1₂O₃ 0.42, P₂O₅ 2.56, As₂O₅ 13.69, CO₂ 0.7, S0₃ 6.33, H₂O 17.7 percent, sum 99.50. The empirical cell contents are Cu_8.8Al_0.1(AsO₄)_1.48(PO₄)_0.43(SO₄)_0.94(CO₃)_0.19(OH)₁₀·6.8H₂O, with an ideal formula of Cu₉(AsO₄)₂(SO₄)(OH)₁₀·7H₂O. The crystals are blades, flattened on {010} and elongated parallel to c. The mineral is orthorhombic with a probable space group of P2₁22. The cell dimensions are a = 14.98(1), b = 14.223(8), and c = 6.018(8)A; Z = 2, D (meas) = 3.09. The strongest lines of the X-ray power pattern (30 given) are 14.30 (100)(010); 10.38 (24)(110); 7.14 (10)(020); 6.42 (8)(120); 4.52 (60)(130); 4.00 (21)(230); 2.849 (19)(050); 2.798 (8)(150). The refractive indices are α = 1.650, β = 1.704, γ = 1.712, 2V_α = 60°, and no observable dispersion of the optic axes. The optic plane is parallel to {100}, X = b, Y = a, and Z = c; X pale green, Y yellow-green, and Z blue-green with Z > Y > X. The mineral dissolves readily in dilute HCl with the evolution of CO₂ bubbles. The name honors John L. Parnau, a mineral collector of Sunnyvale, California, who was the first to find the mineral.

Goudeyite is the Al analog of agardite and is therefore a new member of the mixite group. It occurs as yellow-green hair-like crystals, encrusting fractures and as cross-fiber veinlets. Microprobe analyses with separate determinations for H₂O give the following composition: CaO 1.37, CuO 46.77, Al₂O₃ 4.00, Y₂O₃ 3.40, P₂O₅ 4.55, As₂O₆ 27.85, H₂O 11.0 percent, sum 98.94. This corresponds to Ca_0.24Cu_5.80Al_0.77Y_0.29 (AsO₄)_2.40(PO₄)_0.63(OH)_6.17·2.95H₂O and an ideal formula Cu₆Al(AsO₄)₃(OH)₆·3H₂O. The crystals are hexagonal prisms up to 0.5 mm in length and 2 μm in diameter. The X-ray powder pattern was indexed by analogy with agardite, giving the cell dimensions a = 13.472(1) and c = 5.902(4)A; Z = 2, D (meas) = 3.50. The strongest lines of the X-ray powder pattern (30 given) are 11.63 (100)(100); 4.41 (43)(210); 3.53 (15)(211); 3.367 (20)(220); 3.235 (46)(310); 2.920 (50)(400); 2.677 (42)(320); 2.546 (40)(410). The refractive indices are ω = 1.704 and ϵ = 1.765; ω is pale yellow-green and ϵ is green with ϵ > ω. The mineral dissolves slowly in dilute HC1. The name honors Hatfield Goudey, a mining geologist and mineral collector of San Mateo, California.

Both minerals generally occur alone on limonite-stained fracture surfaces, but other secondary minerals within several meters include divenite, clinoclase, cornwallite, strashimirite, scorodite, pharmacosiderite, arthurite, metazeunerite, chrysocolla, spangolite, chalcophyllite, malachite, azurite, chalcanthite, and bronchantite.