Search

Wortupaite (IMA2022–107) is a new hydrated magnesium nickel tellurite mineral with a zemannite-like structure, described from the Wortupa gold mine, South Australia, Australia. Wortupaite forms needles up to 25 μm in length, generally clustered and sometimes in blocky masses of shorter (10‒15 μm) crystals. Wortupaite is found growing on melonite, from which the component nickel and tellurium are derived, and is associated with calcite. The strongest powder diffraction lines are [ d obsÅ(I obs)(hkl)]: 8.059 (93) (100), 4.034 (92) (200), 2.832 (43) (211 and 121), 2.769 (100) (202) and 1.920 (45) (213 and 123). The empirical formula of wortupaite as determined by electron probe microanalysis is (Mg0.57Ni0.39Mn0.04)Σ1(Ni2+1.87Fe3+0.13)Σ2(Te4+O3)3⋅3H2O, simplified to the ideal formula of MgNi2+2(Te4+O3)3⋅3H2O with H2O content calculated from the crystal structure. The average crystal structure of wortupaite was determined by single-crystal X-ray diffraction with synchrotron radiation (R 1 = 0.0558 for 100 independent reflections). Wortupaite is hexagonal, crystallising in the space group P 63/ m, with a = 9.2215(13) Å, c = 7.5150(15) Å, V = 553.43(19) Å3 and Z = 2. Wortupaite has a microporous structure, with the negatively charged zemannite-like framework formed by Te4+O3 trigonal pyramids and Ni2+O6 octahedra. For charge balance, Mg2+ and Ni2+ dominant sites are assumed to be located on central sites in the channels, coordinated by 6 H2O groups. An OW site was refined around the Mg2+ dominant site, but OW position(s) were not locatable around the Ni2+ dominant site. A discussion of the different models for crystallographic arrangement of channel species is provided, taking into account possible Fourier truncation effects. Unlike the other four minerals with zemannite-like structures which have a near 50% split of divalent and trivalent framework cations, wortupaite is the first natural phase to have only divalent cations in the framework sites. [ABSTRACT FROM AUTHOR]

Reproduced with permission Bulk uranium contents of several different varieties of Lake Boga fluorapatite crystals were determined by isotope dilution mass spectrometry (Mills [7]). Fluorapatite crystals were first recorded in the Lake Boga Granite, in northern Victoria, Australia, in 1941, some fifteen years after a small quarrying operation was established to crush the granite for aggregate (Hills [6]; Birch [2]). Interpenetrating fluorapatite crystals showing characteristic zoning in blue shades, larger crystal 2.5 cm across, with schorl, Lake Boga. Conclusion The Lake Boga fluorapatite crystals are not only attractive in their own right, but they also preserve a record of fluctuating uranium, manganese, and strontium contents in the late-stage hydrothermal fluids circulating within the upper levels of the cooling granite. [Extracted from the article]

Metanatroautunite, Na[(UO2)(PO4)](H2O)3, from the Lake Boga granite, Victoria, Australia, has tetragonal symmetry, space group P4/ncc, with the unit-cell parameters: a = 6.9935(7), c = 17.5101(12) Å, V = 856.40(13) ų, and Z = 4. The crystal structure has been solved and refined to R1 = 0.0398 for 368 unique reflections [F > 4σ(F)] and 0.0456 for all 496 unique reflections. Metanatroautunite has an almost identical corrugated polyhedral sheet to meta-autunite-group minerals, consisting of corner-sharing uranyl square pyramids and phosphate tetrahedra. Hydrogen bonds (and cation-oxygen bonds) link the water molecules in the interlayer into square-planar sets, which are connected together creating 8-membered arrays. Metanatroautunite is identical to synthetic Na[(UO2)(PO4)](H2O)3. [ABSTRACT FROM AUTHOR]

Stichtite, ideally Mg6Cr2CO3(OH)16⋅4H2O, from Stichtite Hill, Tasmania, Australia, and barbertonite, also ideally Mg6Cr2CO3(OH)16⋅4H2O, from the Kaapsehoop asbestos mine, South Africa, have been studied by powder X-ray diffraction and their structures have been refined using the Rietveld method. Stichtite from Stichtite Hill crystallizes in the rhombohedral space group R3̄m, with unit-cell parameters a = 3.09575(3) and c = 23.5069(6) Å, V = 195.099(6) ų, with Z = 3/8. Barbertonite from the Kaapsehoop asbestos mine crystallizes in the hexagonal space group P63/mmc. The co-type specimens of barbertonite were found to be intergrown mixtures consisting of barbertonite and stichtite. Unit-cell parameters of barbertonite from the co-type specimens were a = 3.09689(6), c = 15.6193(8) Å, and V = 129.731(8) ų and a = 3.09646(6), c = 15.627(1) Å V = 129.76(1) ų, and Z = 1/4. Rietveld refinements of both stichtite and barbertonite show that they are polytypes rather than polymorphs and do not represent distinct mineral species. Several possible nomenclature systems are discussed for the naming of hydrotalcite minerals and groups. Raman band assignments are also presented for stichtite from Stichtite Hill. Stichtite and hydrotalcite minerals make up a large proportion of the ore at the Mount Keith nickel mine in Western Australia. Bulk powder diffraction shows the ore contains 6.1 wt% stichtite and 5.6 wt% iowaite. Hydrotalcite group minerals provide an important potential reservoir of CO2. At Mount Keith, the amount of CO2 mined as stichtite could exceed 45 000 metric tons per year, while exchange of Cl for CO3 could fix in excess of 40 000 metric tons CO2 per year if end-member iowaite is reacted to form pyaroaurite. [ABSTRACT FROM AUTHOR]

Lakebogaite, ideally CaNaFe23+H(UO2)2(PO4)4(OH)2(H2O)8, is a new Ca-Na--Fe uranyl phosphate 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 saléeite on a matrix of microcline, albite, smoky quartz, and muscovite. Lakebogaite occurs as bright lemon-yellow transparent prismatic crystals up to 0.4 mm across. The crystals have a vitreous luster and a pale yellow streak. Mohs 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: nα = 1.650(2)-1.652(2), nβ = 1.660(4)-1.664(3), nγ = 1.681(3)-1.686(2), measured using white light, and with 2Vmeas = 80-85° and 2Vcalc = 70-74°. Orientation: Y = b; crystals are elongated along [010], 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)Σ1.90(Fe1.853+Al0.30)Σ2.15(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) Å, β = 115.692(1)°, V = 2349.3(7) ų, Z = 4. The seven strongest reflections in the powder X-ray diffraction pattern are [dobs in Å (I) (hkl)]: 6.60 (100) (110), 3.16 (40) (514̄, 604̄), 4.07 (20) (404̄), 3.80 (20) (314̄), 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 R1 = 0.038 on the basis of 5222 unique reflections with F > 4σF. It comprises pairs of edge-shared UO7 pentagonal bipyramids that are inter-linked via corner-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 corner-sharing between the PO4 tetrahedra and Fe3+O4(OH)2 octahedra. The octahedra join together by corner-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. [ABSTRACT FROM AUTHOR]

The mineral peisleyite has been studied using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscope (SEM) photomicrographs reveal that the peisleyite morphology consists of an array of small needle-like crystals of around 1 microm in length with a thickness of less than 0.1 microm. Raman spectroscopy in the hydroxyl stretching region shows an intense band at 3506 cm(-1) assigned to the symmetric stretching mode of the OH units. Four bands are observed at 3564, 3404, 3250 and 3135 cm(-1) in the infrared spectrum. These wavenumbers enable an estimation of the hydrogen bond distances 3.052(5), 2.801(0), 2.705(6) and 2.683(6)A. Two intense Raman bands are observed at 1023 and 989 cm(-1) and are assigned to the SO(4) and PO(4) symmetric stretching modes. Other bands are observed at 1356, 1252, 1235, 1152, 1128, 1098 and 1067 cm(-1). The bands at 1067 cm(-1) is attributed to AlOH deformation vibrations. Bands in the low wavenumber region are assigned to the nu(4) and nu(2) out of plane bending modes of the SO(4) and PO(4) units. Raman spectroscopy is a useful tool in determining the vibrational spectroscopy of mixed hydrated multianion minerals such as peisleyite. Information on such a mineral would be difficult to obtain by other means.