New Minerals from the Redmond Mine, North Carolina, USA: VI. Boojumite and Kennygayite, Two New Minerals with Structures Based on Chains of Oxocentered OPb₄ TETRAHEDRA

The new minerals boojumite, Pb₈O₄(OH)₂(S₂O₃)₃ (IMA2022-028), and kennygayite, [Pb₄O₂(OH)₂](SO₄) (IMA2022-032), 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. Boojumite was found in close association with bechererite, caledonite, cubothioplumbite, hexathioplumbite, hydroredmondite, redmondite, steverustite, and sulfatoredmondite. Kennygayite was found in close association with bechererite, chenite, cherokeeite, redmondite, sidpietersite, and steverustite. Boojumite properties: yellow prisms or blades to about 0.3 mm long; very pale yellow streak; adamantine luster; brittle; Mohs hardness ∼ 2½; irregular fracture; no cleavage; 6.619 g/cm³ calculated density; biaxial (−) with α = 2.0350(calc.), β = 2.0710(calc.), γ = 2.0725(calc.), 2V = 23(3)°. Kennygayite properties: colorless to pale yellow wedges and lozenge-shaped wafers, up to about 1 mm across; white streak; adamantine luster; brittle; Mohs hardness ∼ 2½; irregular, stepped fracture; perfect cleavage on {001}; 7.078 g/cm³ calculated density; biaxial (−) with α = 1.98(calc.), β = 2.01 (est.), γ = 2.09 (calc.), 2V = 58(5)°. Electron probe microanalyses provided the empirical formulae Pb₈O₄(OH)₂(S₂O₃)_2.57(SO₄)_0.43 and [Pb₄O₂(OH)₂](SO₄)_0.87(S₂O₃)_0.13 for boojumite and kennygayite, respectively. Boojumite is orthorhombic, Pnma, a = 14.0103(8), b = 20.5529(10), c = 7.2668(5) Å, V = 2092.5(2) ų, and Z = 4. Kennygayite is triclinic, P⁠, a = 6.3785(5), b = 7.4519(6), c = 10.3112(8) Å, α = 75.234(5), β = 79.388(6), γ = 88.175(6)°, V = 465.76(6) ų, Z = 2. The structures of boojumite (R₁ = 0.057 for 1538 I > 2σI) and kennygayite (R₁ = 0.046 for 2419 I > 2σI) are both based on chains of edge-sharing oxocentered OPb₄ tetrahedra. The chain in boojumite is sinuous, whereas that in kennygayite is zig-zag.