BAMFORDITE, FE3-DOT-H2O, A NEW HYDRATED IRON MOLYBDENUM OXYHYDROXIDE FORM QUEENSLAND, AUSTRALIA - DESCRIPTION AND CRYSTAL-CHEMISTRY(MO2O6(OH)(3)CENTER)

Bamfordite from the abandoned W-Mo-Bi mines at Bamford, Queensland, Au stralia, is a new hydrated iron molybdate with a unique structure. Thi s mineral formed by oxidation of molybdenite, MoS2, in the presence of strongly acidic solutions. It occurs as microcrystalline aggregates o f tabular triclinic crystals between 0.005 and 0.05 mm long. The aggre gates are apple-green with an earthy luster and greenish yellow streak . Crystals are transparent, with pale to moderate yellow-green pleochr oism. They show principal forms {001}, {100}, {010}, {110}, {<1(1)over bar>0}, and prominent (100) cleavage traces. The Mohs hardness is 2-3 and the measured density is 3.620 g/cm(3) (calculated density is 3.61 6 g/cm(3)). Crystals are biaxial negative and length slow, with RIs of alpha = 1.91, beta = 2.03, and gamma = 2.11, and 2V approximate to 90 degrees. Chemical analysis yielded an empirical formula of Fe1.003+Mo 2.01W0.03 P0.02O10H4.62, calculated on the basis of ten O atoms. The s implified formula is Fe3+Mo2O6 (OH)(3) . H2O, chosen on the basis of c rystal-structure determination and Mossbauer spectroscopy results. Uni t-cell parameters calculated both from the X-ray powder and single-cry stal diffraction data are a = 5.889(5), b = 7.545(5), c = 9.419(5) Ang strom; alpha = 71.46(4)degrees, beta = 83.42(4)degrees, gamma = 72.78( 4)degrees; V = 378.9(4) Angstrom(3); Z = 2; P1 or <P(1)over bar>. The crystal structure was solved in P1 using direct methods and Fourier te chniques. The final refinement based on 1486 observed reflections [I > 2.00 sigma I] converged to R = 0.05 and R-w = 0.038. The bamfordite c rystal structure contains groups of four MoO6 octahedra, linked by edg e-sharing, which in turn are linked through corner-sharing to pairs of FeO6 octahedra thereby forming infinite sheets parallel to (100). The se sheets are stepped and linked by hydrogen bonding. No other molybde num oxides have this or a similar structure, instead molybdates such a s wulfenite, PbMoO4, are based on tetrahedrally coordinated molybdenum .