Cloncurryite, Cu0.56(VO)0.44Al2(PO4)2(F,OH)2.5H2O, a new mineral from the Great Australia mine, Cloncurry, Queensland, Australia, and its relationship to nevadaite

Cloncurryite, Cux(VO)(1-x)Al2(PO4)2(F,OH02nH2), with x=0.56, F≈OH and n≈5 (IMA 2005-060), is a new mineral from the Great Australia mine, Cloncurry, Queensland, Australia. The name is derived from the locality. It occurs as aggregates of slender, sky-blue needles in silicified goethite-hematite gossan associated with malachite, pseudomalachite, cuprite and native copper. Cloncurry is monoclinic, space group P21/c, with a=4.9573(2), b=12.1824(4), c=18.9749(8) Å, ß=90.933(6)°, V=1145.78(14) Å3, Z=4, Dc=2.525 g cm¯³, based on the formula Cu0.56(VO)0.44Al1.98Fe0.02(PO4)2F(OH0.5H2) (analysis and single-crystal X-ray structure), and a=4.961(2), b=12.181(4), c=18.974(7) Å, ß=90.96(4)°, V=1146.4(11) ų, Z=4 (from least-squares refinement of powder diffraction data). The a:b:c ratio calculated from unit-cell parameters is: 0.4069:1:1.5576. The ten strongest lines in the X-ray powder diffraction pattern [d in Å(I)(hkl)] are: 6.101(100)(020), 5.621(91)(013), 9.515(67)(002), 3.976(21)(031), 3.338(21)(14), 4.753(17)(004), 3.163(17)(006), 3.047(13)(040), 2.903(12)(115) and 2.808(10)(026). An average of 10 microprobe analyses (wt%) gave CuO 10.29; VO28.32; Al2O3 23.63; Fe2O3 0.32; P2O3 0.32; P2O5 32.54; F 4.34; H2O (by difference) 22.4, less O=F -1.83; total, 100.00. No other metallic elements were detected. The derived empirical formula (based on 2 PO, groups pfu and F + OH = 2 pfu) is [Cu0.56(VO)0.44]Σ2.04(PO4)2F1.00.4.92H2O and the symplified formula is [Cu0.56(VO)0.44]Al2(PO4)2(F,OH)2.5H2), with F ≈ OH. The formula is entirely consistent with the results of the single-crystal X-ray structure analysis. Cloncurryite occurs as sky-blue clusters and radiating sprays of extremely acicular prismatic crystals, in a ferruginous, silicified gossan matrix. Isolated needles less than 1 mm long and less than 0.03 mm in thickness are very pale sky-blue in colour and when small appear colourless. Crystals are non-fluorescent, have a white streak and are transparent with a vitreous lustre. Mohs hardness is 2, fracture is uneven and no cleavage was observed. Acicular prisms are elonated along the axis with forms {010} and {001} and twinning on {100}. Cloncurryite is biaxial (-), with ά=1.548(2), y=1.550(2) (white light), 2V (calc.)=56°. Dispersion, r<v, is very weak. The orientation is X=a, Y≈b, Z≈c. Pleochroism is faint, but distinct pale blue (ß,y) to very pale greenish blue (ά). A characteristic, strong vanadyl (VO2+) stretch is present in the Raman spectrum at 1044cm-1. The structure of cloncurryite is related to that of the orthorhombic mineral nevadaite, but can be conveniently distinguished from the latter by analysis, the presence of VO2+ (in cloncurryite) and a careful examination of X-ray powder diffraction data.