Bamfordite, Fe3+Mo2O6(OH)3·H 2O, a new hydrated iron molybdenum oxyhydroxide from Queensland, Australia: Description and crystal chemistry

William D. Birch, Allan Pring, E. Maude Mcbriar, Bryan M. Gatehouse, Catherine A. Mccammon

Research output: Contribution to journalArticle

6 Citations (Scopus)

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. MoS2, 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/cm3 (calculated density is 3.616 g/cm3). Crystals are biaxial negative and length slow, with RIs of α = 1.91, β = 2.03, and γ = 2.11, and 2V ≈ 90°. Chemical analysis yielded an empirical formula of Fe3+1.00 Mo2.01W0.03 P0.02O10H4.62, calculated on the basis of ten O atoms. The simplified formula is Fe3+Mo2O6 (OH)3·H2O, chosen on the basis of crystal-structure determination and Mössbauer 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) Å; α = 71.46(4)°, β = 83.42(4)°, γ = 72.78(4)°; V = 378.9(4) Å3; 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 σI] converged to R = 0.05 and Rw = 0.038. The bamfordite crystal structure contains groups of four MoO6 octahedra, linked by edge-sharing, which in turn are linked through corner-sharing to pairs of FeO6 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, PbMoO4, are based on tetrahedrally coordinated molybdenum.

Original languageEnglish
Pages (from-to)172-177
Number of pages6
JournalAmerican Mineralogist
Volume83
Issue number1-2
DOIs
Publication statusPublished - 1 Jan 1998
Externally publishedYes

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