New Minerals from the Redmond Mine, North Carolina, USA: V. Finescreekite and Hayelasdiite, Two New Thiosulfate Minerals Containing Cubane-Like Pb4O4 Structural Units

Abstract

The new minerals finescreekite, [Pb4(OH)4](S2O3)2 (IMA2022–030), and hayelasdiite, [Pb4O1.5(OH)2.5]2[Cu+5(S2O3)4(S2O2OH)2(H2O)]·4H2O (IMA2022–021), were found in the Redmond mine, Haywood County, North Carolina, USA, where they occur in a highly unusual secondary assemblage that comprises a variety of rare Pb-Zn-Cu sulfates, thiosulfates, and carbonates. Finescreekite was found in close association with anglesite, cubothioplumbite, redmondite, and steverustite. Hayelasdiite was found in close association with anglesite and steverustite. Finescreekite properties: colorless tablets to about 1.5 mm across; white streak; resinous to adamantine luster; brittle; Mohs hardness ∼ 2½; curved, stepped fracture; excellent cleavage on {001}, fair on {100}, {010}, and {110}; 5.675 g/cm3 calculated density; biaxial (−) with α = 2.00(1), β = 2.04(calc), γ = 2.065(calc), 2V = 75.9(5)°. Hayelasdiite properties: colorless prisms and blades to about 0.5 mm in length; white streak; vitreous to subadamantine luster; brittle; Mohs hardness ∼ 2½; curved fracture; perfect cleavage on {010}; 4.909 g/cm3 calculated density; biaxial (−) with α = 1.89(1), β = 1.95(calc), γ = 1.97(calc), 2V = 58(5)°. Electron probe microanalyses provided the empirical formulae [Pb4(OH)4](S2O3)1.76(SO4)0.24 and [Pb4.00O1.5(OH)2.5]2[Cu+5.00(S2O3)3.24(SO4)0.76(S2O2OH)2(H2O)]·4H2O for finescreekite and hayelasdiite, respectively. Finescreekite is Orthorhombic, P212121, a = 8.2330(9), b = 10.7128(13), c = 14.8256(13) Å, V = 1307.6(2) Å3, and Z = 4. Hayelasdiite is triclinic, P1̄, a = 7.52089(15), b =14.9345(3), c = 17.9895(13) Å, α = 106.727(8), β = 90.966(6), γ = 90.031(6)°, V = 1934.79(16) Å3, and Z = 2. The structures of finescreekite (R1 = 0.061 for 1440 I > 2σI) and hayelasdiite (R1 = 0.055 for 5636 I > 2σI) both contain cubane-like Pb4O4 clusters, [Pb4(OH)4]4+ in finescreekite and [Pb4O1.5(OH)2.5]2.5+ in hayelasdiite. The structure of hayelasdiite also contains a decorated double chain with the formula [Cu+5(S2O3)4(S2O2OH)2(H2O)]5−.