New Minerals from the Redmond Mine, North Carolina, USA: VII. Zincochenite, the Zn Analogue of Chenite

The new mineral zincochenite, Pb₄Zn(OH)₆(SO₄)₂ (IMA2022-025), was found in the Redmond mine, Haywood County, North Carolina, USA, where it occurs in a highly unusual secondary assemblage that comprises a variety of rare Pb-Zn-Cu sulfates, thiosulfates, and carbonates. Zincochenite was found in vugs in massive galena-sphalerite-chalcopyrite-quartz in close association with bechererite, chenite, cherokeeite, elyite, lanarkite, and steverustite. Zincochenite crystals vary in habit including tablets, blades, and prisms, up to about 0.5 mm in maximum dimension. Crystals always occur in tightly intergrown subparallel clusters. The color is most commonly light blue, the streak is white, and the luster is vitreous to resinous. The mineral is brittle with curved and irregular fracture and one fair cleavage, probably on ⁠. The Mohs hardness is about 3½. The calculated density is 5.939 g/cm³. The mineral is biaxial (−) with α = 1.875(5), β = 1.900(5), γ = 1.915(5). The 2V is 78.4(5)° with strong r > v dispersion. The partially determined optical orientation is Y ≈  and there is no pleochroism. Electron microprobe analyses provided the empirical formula Pb_4.00(Zn_0.94Cu²⁺_0.06)_Σ1.00(SO₄)_1.81(S₂O₃)_0.19(OH)₆. Zincochenite is triclinic, ⁠, a = 5.883(4), b = 7.938(5), c = 7.948(5) Å, α = 110.511(12), β = 98.497(10), γ = 100.152(8)°, V = 333.2(3) ų, and Z = 1. Zincochenite is isostructural with chenite. In the crystal structure (R₁ = 0.0874 for 936 I > 2σI), short bonds between the Pb atoms and OH groups define a chain along [011] and these chains are bridged by ZnO₂(OH)₄ octahedra to form sheets parallel to ⁠. SO₄ tetrahedra decorate both sides of the sheets. The sheets are linked together in the  direction via long Pb–O bonds and hydrogen bonds.