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

The 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 [Pb_2.00Zn_1.00(OH)₄](SO₄)_0.85(S₂O₃)_0.15·H₂O and [Pb_8.14(Zn_2.52Cu²⁺_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) ų, 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) ų, 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⁺.