Browsing by Author "Mills, SJ"

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    Bulachite, [Al6(AsO4)3(OH)9(H2O)4]⋅2H2O from Cap Garonne, France: crystal structure and formation from a higher hydrate
    (Cambridge University Press, 2020-06-30) Grey, IE; Yoruk, E; Kodjikian, S; Klein, H; Bougerol, C; Brand, HEA; Bordet, P; Mumme, WG; Favreau, G; Mills, SJ
    Bulachite specimens from Cap Garonne, France, comprise two intimately mixed hydrated aluminium arsenate minerals with the same Al:As ratio of 2:1 and with different water contents. The crystal structures of both minerals have been solved using data from low-dose electron diffraction tomography combined with synchrotron powder X-ray diffraction. One of the minerals has the same powder X-ray diffraction pattern (PXRD) as for published bulachite. It has orthorhombic symmetry, space group Pnma with unit-cell parameters a = 15.3994(3), b = 17.6598(3), c = 7.8083(1) Å and Z = 4, with the formula [Al6(AsO4)3(OH)9(H2O)4]·2H2O. The second mineral is a higher hydrate with composition [Al6(AsO4)3(OH)9(H2O)4]·8H2O. It has the same Pnma space group and unit-cell parameters a = 19.855(4), b = 17.6933(11) and c = 7.7799(5) Å i.e. almost the same b and c parameters but a much larger a parameter. The structures are based on polyhedral layers, parallel to (100), of composition [Al6(AsO4)3(OH)9(H2O)4] and with H-bonded H2O between the layers. The layers contain [001] spiral chains of edge-shared octahedra, decorated with corner connected AsO4 tetrahedra that are the same as in the mineral liskeardite. The spiral chains are joined together by octahedral edge-sharing to form layers parallel to (100). Synchrotron PXRD patterns collected at different temperatures during heating of the specimen show that the higher-hydrate mineral starts transforming to bulachite when heated to 50°C, and the transformation is complete between 75 and 100°C. © 2020 The Mineralogical Society of Great Britain and Ireland .
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    Crystal structure of posnjakite formed in the first crystal water-cooling line of the ANSTO Melbourne Australian Synchrotron MX1 Double Crystal Monochromator
    (International Union of Crystallography (IUCr), 2020-06-30T14:00:00Z) Mills, SJ; Aishima, J; Aragao, D; Caradoc-Davies, TT; Cowieson, NP; Gee, CL; Ericsson, D; Harrop, SJ; Panjikar, S; Smith, KML; Riboldi-Tunnicliffe, A; Williamson, R; Price, JR
    Exceptionally large crystals of posnjakite, CuSO(OH)(HO), formed during corrosion of a Swagelock(tm) Snubber copper gasket within the MX1 beamline at the ANSTO-Melbourne, Australian Synchrotron. The crystal structure was solved using synchrotron radiation to = 0.029 and revealed a structure based upon [Cu(OH)(HO)O] sheets, which contain Jahn-Teller-distorted Cu octa-hedra. The sulfate tetra-hedra are bonded to one side of the sheet corner sharing and linked to successive sheets extensive hydrogen bonds. The sulfate tetra-hedra are split and rotated, which enables additional hydrogen bonds. © Mills et al. 2020.
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    Galeaclolusite, [Al6(AsO4)3(OH)9(H2O)4]⋅8H2O, a new bulachite-related mineral from Cap Garonne, France
    (Cambridge University Press, 2020-12-04) Grey, IE; Favreau, G; Mills, SJ; Mumme, WG; Bougerol, C; Brand, HEA; Kampf, AR; MacRae, CM; Shanks, FL
    Galeaclolusite, [Al6(AsO4)3(OH)9(H2O)4].8H2O, is a new secondary hydrated aluminium arsenate mineral from Cap Garonne, Var, France. It forms crusts and spheroids of white fibres up to 50 μm long by 0.4 μm wide and only 0.1 μm thick. The fibres are elongated along [001] and flattened on (100). The calculated density is 2.27 g.cm-3. Optically, galeaclolusite is biaxial with α = 1.550(5), β not determined, γ = 1.570(5) (white light) and partial orientation: Z = c (fibre axis). Electron microprobe analyses coupled with crystal structure refinement results gives an empirical formula based on 33 O atoms of Al5.72Si0.08As2.88O33H34.12. Galeaclolusite is orthorhombic, Pnma, with a = 19.855(4), b = 17.6933(11), c = 7.7799(5) A, V = 2733.0(7) Aand Z = 4. The crystal structure of galeaclolusite was established from its close relationship to bulachite and refined using synchrotron powder X-ray diffraction data. It is based on heteropolyhedral layers, parallel to (100), of composition Al6(AsO4)3(OH)9(H2O)4 and with H-bonded H2O between the layers. The layers contain [001] spiral chains of edge-shared octahedra, decorated with corner-connected AsO4 tetrahedra, that are the same as in the mineral liskeardite. © 2020. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland.
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    New type of cubic-stacked layer structure in anthoinite, AlWO3(OH)(3)
    (Mineralogical Society of America, 2010-04) Grey, IE; Madsen, IC; Mills, SJ; Hatert, F; Peterson, VK; Bastow, TJ
    Anthoinite, AlWO3(OH)3, from the Mt. Misobo Mine, Democratic Republic of the Congo, has triclinic symmetry with cell parameters a = 8.196(1) Å, b = 9.187(1) Å, c = 11.316(1) Å, = 92.82(1)°, β = 94.08(1)°, = 90.23(1)°, space group ґI, Z = 8. The structure was solved by applying ab initio structure solution methods (Reverse Monte Carlo/Simulated Annealing) to both X-ray and neutron powder diffraction data and was refined using the Rietveld method. The structure is built up of two types of M4(O,OH)16 planar tetrameric clusters of edge-sharing octahedra, one containing predominantly Al and the other predominantly W. The Al-rich and W-rich clusters interconnect via corner sharing to form stepped layers parallel to (001). The layers are held together by strong hydrogen bonding. The structure can be described as a rocksalt derivative structure, with the close-packed anion layers parallel to (012), and with Al and W atoms ordered into one third of the octahedral sites within the cubic close-packed anion lattice. The structure is complicated by partial disorder between Al and W in the tetrameric clusters and associated disorder in the H atom sites. Infrared and 27Al MAS NMR results are also presented for anthoinite. © 2010, Mineralogical Society of America