Crystal structure of tooeleite, Fe6(AsO3)4SO4(OH)4{middle dot}4H2O, a new iron arsenite oxyhydroxy-sulfate mineral relevant to acid mine drainage

摘要

The crystal structure of tooeleite, Fe₆(AsO₃)₄(SO₄)(OH)₄·4H₂O, has been solved from high-resolution synchrotron XRD powder data recorded on a sample from Tooele county, Utah. The structure is monoclinic, space group C2/m, a = 8.9575(1), b = 6.4238(1), c = 9.7912(1) Å, ß = 96.032(1)°, V = 560.27(3) Å3, d_calc = 3.16 g/cm3. The structure was solved by direct methods and atomic positions, site occupancies, and isotropic displacement parameters were refined by the Rietveld method. The AsO₃ pyramids bond to FeO₆ octahedra by both edge- and corner-linkage, forming layers that intercalate SO₄ groups. Assignment of structural H₂O and OH groups were done from bond-valence analysis. Tooeleite is the only arsenite-sulfate mineral known and has been recently identified as the main constituent of stromatolite-like deposits in the Carnoulès acid mine, Gard, France.