Refinement of the crystal structure of zoned philipsbornite–hidalgoite from the Tsumeb mine, Namibia, and hydrogen bonding in the D²⁺$G33+$(T⁵⁺O₄)(TO₃OH)(OH)₆ alunite structures

The crystal structure of zoned philipsbornite hidalgoite, hexagonal (rhombohedral), R3İm, Z = 3: a = 7.1142(4), c = 17.0973(9) Å, V = 749.4(1) ų, from the Tsumeb mine, Namibia, has been refined to R₁ = 1.68% for 301 unique reflections collected on a Bruker D8 three-circle diffractometer equipped with a rotating-anode generator, multilayer optics and an APEX-II CCD detector. Chemical analysis by electron microprobe showed zoned crystals with a rim enriched in S and Fe relative to the core. The core composition is SO₃ 3.31, As₂O₅ 30.57, Al₂O₃ 23.05, FeO 1.44, PbO 33.94, H₂O_calc 9.58, total 101.79 wt.%, corresponding to $Pb0.992+$(Al_2.92$Fe0.132+$⁠)(AsO₄)[(As_0.72S_0.27)O_3.14(OH)_0.85](OH)₆; and the rim composition is SO₃ 8.88, As₂O₅ 22.63, Al₂O₃ 22.90, FeO 2.57, PbO 34.91, H₂O_calc 9.27, total 101.16 wt.%, corresponding to $Pb0.992+$(Al_2.85$Fe0.232+$⁠)(AsO₄)[(As_0.25S_0.70)O_3.30(OH)_0.50](OH)₆. Philipsbornite hidalgoite has the alunite-type structure, sheets of corner-sharing octahedra, decorated on top and bottom by [(As,S)O₄] and (AsO₃OH) tetrahedra, that are linked into a three-dimensional structure by [12]-coordinated Pb²⁺ cations and hydrogen bonds. A new hydrogen-bonding scheme for the D²⁺$G33+$(T⁵⁺O₄)(TO₃OH)(OH)₆ minerals is proposed.