Showing papers by "Bryan M. Gatehouse published in 1998"
TL;DR: Bamfordite as discussed by the authors is a new hydrated iron molybdate with a unique structure, which contains groups of four MoO 6 octahedra, linked by edge-sharing, which in turn are linked through corner-sharing to pairs of FeO6 octahedral, thereby forming infinite sheets parallel to (100).
Abstract: Bamfordite from the abandoned W-Mo-Bi mines at Bamford, Queensland, Australia, is a new hydrated iron molybdate with a unique structure. This mineral formed by oxidation of molybdenite, MoS 2 . in the presence of strongly acidic solutions. It occurs as microcrystalline aggregates of tabular triclinic crystals between 0.005 and 0.05 mm long. The aggregates are apple-green with an earthy luster and greenish yellow streak. Crystals are transparent, with pale to moderate yellow-green pleochroism. They show principal forms {001}, {100}, {010}, {110}, {110}, and prominent (100) cleavage traces. The Mohs hardness is 2-3 and the measured density is 3.620 g/cm 3 (calculated density is 3.616 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 nearly equal 90 degrees . Chemical analysis yielded an empirical formula of Fe (super 3+) (sub 1.00) Mo (sub 2.01) W (sub 0.03) P (sub 0.02) O 10 H (sub 4.62) , calculated on the basis of ten O atoms. The simplified formula is Fe (super 3+) Mo 2 O 6 (OH) 3 .H 2 O, chosen on the basis of crystal-structure determination and Mossbauer spectroscopy results. Unit-cell parameters calculated both from the X-ray powder and single-crystal diffraction data are a = 5.889(5), b = 7.545(5), c = 9.419(5) Aa; alpha = 71.46(4) degrees , beta = 83.42(4) degrees ; gamma = 72.78(4) degrees ; V = 378.9(4) Aa 3 ; Z = 2; P1 or P1. The crystal structure was solved in P1 using direct methods and Fourier techniques. 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 crystal structure contains groups of four MoO 6 octahedra, linked by edge-sharing, which in turn are linked through corner-sharing to pairs of FeO 6 octahedra thereby forming infinite sheets parallel to (100). These sheets are stepped and linked by hydrogen bonding. No other molybdenum oxides have this or a similar structure, instead molybdates such as wulfenite, PbMoO 4 , are based on tetrahedrally coordinated molybdenum.
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