New Minerals from the Redmond Mine, North Carolina, USA: III. Cherokeeite and Cuprocherokeeite, Two New Minerals Containing [Pb2(Zn,Cu2+)(OH)4]2+ Chains

Abstract

AbstractThe new minerals cherokeeite, [Pb2Zn(OH)4](SO4)·H2O (IMA2022-016), and cuprocherokeeite, [Pb8Zn3Cu2+(OH)16](SO4)4·4H2O (IMA2022-086), were found in the Redmond mine, Haywood County, North Carolina, USA, where they occur together in a highly unusual secondary assemblage that comprises a variety of rare Pb-Zn-Cu sulfates, thiosulfates, and carbonates. Cherokeeite has the following properties: colorless to pale pink prisms or blades to about 1 mm; white streak; vitreous luster; brittle; Mohs hardness 2½; splintery fracture; at least two perfect cleavages; 5.011 g/cm3 calculated density; biaxial (+) with α = 1.745(5), β = 1.770(5), γ = 1.805(5), and 2V = 85(2)°. Cuprocherokeeite has the following properties: light blue prisms or blades to about 1 mm; very pale bluish-white streak; vitreous luster; brittle; Mohs hardness 2½; irregular, curved fracture; probably two good cleavages; 5.032 g/cm3 calculated density; biaxial (+) with α = 1.760(5), β = 1.770(5), γ = 1.800(5), and 2V (meas.) = 65(3)°. Electron probe microanalyses provided the empirical formulae [Pb2.00Zn1.00(OH)4](SO4)0.85(S2O3)0.15·H2O and [Pb8.14(Zn2.52Cu2+1.34)(OH)16][(SO4)3.07(S2O3)0.93]·4H2O for cherokeeite and cuprocherokeeite, respectively. Cherokeeite is monoclinic, P21/n, a = 17.1697(7), b = 6.47173(19), c = 17.5304(12) Å, β = 115.440(8)°, V = 1759.06(19) Å3, and Z = 8. Cuprocherokeeite is monoclinic, P21/n, a = 12.6828(5), b = 9.4629(5), c = 14.7876(8) Å, β = 94.798(4)°, V = 1768.53(15) Å3, and Z = 2. The structures of cherokeeite (R1 = 0.0425 for 2681 I > 2σI) and cuprocherokeeite (R1 = 0.0741 for 2411 I > 2σI) both contain edge-sharing chains of octahedra decorated by Pb2+ cations, which are strongly bonded to the chains via short Pb–O bonds. In cherokeeite, the octahedral cations are all Zn, whereas in cuprocherokeeite, one in every four cations is Cu2+.