New Minerals from the Redmond Mine, North Carolina, USA: II. Cubothioplumbite and Hexathioplumbite, Two New Minerals Containing the Cubane-Like [Pb₄(OH)₄]⁴⁺ Structural Unit

Abstract

The new minerals cubothioplumbite (IMA2021-091) and hexathioplumbite (IMA2021-092), both with the ideal formula [Pb₄(OH)₄]Pb(S₂O₃)₃, 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. Cubothioplumbite has the following properties: yellow equant crystals to about 0.5 mm; white streak; adamantine luster; brittle; Mohs hardness 3; conchoidal fracture; no cleavage; 5.748 g/cm³ calculated density; isotropic with n > 2.00. Hexathioplumbite has the following properties: colorless hexagonal prisms to about 1 mm; white streak; adamantine luster; brittle; Mohs hardness 2½; curved fracture; no cleavage; 5.531 g/cm³ calculated density; uniaxial (−) with ω = 2.005(5) and ε = 1.995(5). Electron probe microanalyses provided the empirical formulae [Pb₄(OH)₄]Pb(S₂O₃)_2.72(SO₄)_0.28 and [Pb₄(OH)₄]Pb(S₂O₃)_2.68(SO₄)_0.32 for cubothioplumbite and hexathioplumbite, respectively. Cubothioplumbite is cubic, Pa 3⁠, a = 14.9179(13) Å, V = 3319.9(9) ų, and Z = 8. Hexathioplumbite is hexagonal, P6₃, a = 10.7213(10), c = 8.6541(6) Å, V = 861.49(17) ų, and Z = 2. The structures of cubothioplumbite (R₁ = 0.0354 for 1090 I > 2σI) and hexathioplumbite (R₁ = 0.0791 for 1062 I > 2σI) both contain cubane-like [Pb₄(OH)₄]⁴⁺ structural units.

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