Lakebogaite, CaNaFe23+H(UO2)(2)(PO4)(4)(OH)(2)(H2O)(8), a new uranyl phosphate with a unique crystal structure from Victoria, Australia

作者：Mills Stuart J^*; Birch William D; Kolitsch Uwe; Mumme W Gus; Grey Ian E

来源：American Mineralogist, 2008, 93(4): 691-697.

DOI：10.2138/am.2008.2706

• lakebogaite
• new mineral
• uranyl phosphate
• Lake Boga quarry
• north-western Victoria
• Australia
• crystal structure
• (UO2)(2)(PO4)(4) chains

Lakebogaite, ideally CaNaFe23+H(UO2)(2)(PO4)(4)(OH)(2)(H2O)(8) is a new Ca-Na-Fe uranyl phosphate 2 20)8, mineral from a quarry in Upper Devonian granite near Lake Boga, northern Victoria, Australia. it is associated with Na-analogue of meurigite (IMA 2007-024), torbernite, and saleeite on a matrix of microcline, albite, smoky quartz, and muscovite. Lakebogaite occurs as bright lemon-yellow transparent prismatic crystals up to 0.4 min across. The crystals have a vitreous luster and a pale yellow streak. Molis hardness is about 3. The fracture is even to conchoidal. In transmitted light, the mineral is pale yellow with very weak pleochroism: X = yellow, Y = grayish yellow, Z = grayish yellow: dispersion r > v, strong. Lakebogaite crystals are biaxial (+), with slightly variable refractive indices within the ranges: n(alpha) = 1.650(2)-1.652(2), n(beta) = 1.660(4)-1.664(3), n(gamma) = 1.681(3)-1.686(2), measured using white light, and with 2V(meas) = 80-85 degrees and 2V(calc) = 70-74 degrees. Orientation: Y = b; crystals are elongated along [0 10], resulting in straight extinction. The empirical chemical formula (mean of nine electron microprobe analyses) calculated on the basis of 30 anions is (Ca1.00Na0.80Sr0.10)(Sigma 1.90)(Fe1.853+Al0.30)(Sigma 2.15)(UO2)(1.80) (PO4)(4.07)(OH,H2O),(10.12). Lakebogaite is monoclinic, space group Cc, a = 19.6441(5), b = 7.0958(2), c = 18.7029(5) angstrom, beta = 11 5.692(1)degrees, V = 2349.3(7) angstrom(3), Z = 4. The seven strongest reflections in the powder X-ray diffraction pattern are [d(obs) in angstrom (I) (hkl)]: 6.60 (100) (110), 3.16 (40) (51 (4) over bar, 60 (4) over bar), 4.07 (20) (40 (4) over bar), 3.80 (20) (31 (4) over bar), 3.56 (20) (020, 312), 3.31 (20) (114, 220), 2.797 (20) (006). The crystal structure was solved from single-crystal X-ray diffraction data and refined to R, = 0.038 on the basis of 5222 unique reflections with F > 4 alpha F. It comprises pairs of edge-shared UO7 pentagonal bipyramids that are inter-linked via comer-sharing with PO4 tetrahedra, to form chains parallel to the c-axis. Each UO7 polyhedron also shares one of its edges with another PO4 tetrahedron. The (UO2)(2)(PO4)(4) chains are cross-linked via comer-sharing between the PO4 tetrahedra and Fe3+O4(OH)(2) octahedra. The octahedra join together by comer-sharing via OH anions to form chains parallel to b. The Na+ and Ca2+ cations, and 4 water molecules occupy eight-sided channels along [010]. The remaining water molecules occupy large ten-sided channels directed along [001] and intersecting the [010] channels. The mineral is named for the nearest township.

• 出版日期2008-4
• 单位CSIRO