Spriggite, Pb3[(UO2)6O8(OH)2](H2O)3, a new mineral with β-U3O8–type sheets: Description and crystal structure
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Joël Brugger
, Sergey V. Krivovichev
, Peter Berlepsch , Nicolas Meisser , Stefan Ansermet and Thomas Armbruster
Abstract
Spriggite, Pb3[(UO2)6O8(OH)2](H2O)3, is a new hydrated Pb uranyl oxyhydroxide found near Arkaroola, Northern Flinders Ranges, South Australia. The new mineralʼs name honors geologist and conservationist Reginald Claude Sprigg (1919-1994), founder of the Arkaroola Tourist Station. Together with beta-uranophane, soddyite, kasolite, Ce-rich francoisite-(Nd), metatorbernite, billietite, Ba-bearing boltwoodite, schoepite, metaschoepite, and weeksite, spriggite results from the supergene alteration of U-Nb-REE-bearing hydrothermal hematite breccia. Spriggite forms prismatic crystals up to about 150 μm in length and up to 40 μm across. It is transparent, bright orange in color with vitreous luster, biaxial, nmin= 1.807; nmax = 1.891 (NaD, 22.5 °C), non-fluorescent, brittle with an uneven fracture. It has a pale orange streak, Mohsʼ hardness ~4, good cleavage along (100) and Dcalc = 7.64(6) g/ cm3. The empirical formula is (Pb2.77Ca0.06Ba0.04)Σ2.87U6O19.9(OH)2⋅3H2O, and the simplified formula is Pb3[(UO2)6O8(OH)2](H2O)3. Spriggite is monoclinic, C2/c, a = 28.355(9), b = 11.990(4), c = 13.998(4) Å, β = 104.248(5); V = 4613(3) Å3, Z = 8. The strongest eight lines in the powder X-ray diffraction pattern are [d in Å (I)(hkl)]: 6.92(60)(400), 6.02(30)(112̅;020), 3.46(80)(800), 3.10(100)(204;6̅04;33̅2;5̅32), 2̅.74(30)(4̅40), 2.01(30)(336̅), 1.918(60)(10.04̅;14.04̅;11.3̅2;1̅3̅-.31), 1.738(30)(53̅6;1̅1̅.36). The structure has been solved from a crystal twinned on (001) and refined to R1 = 9.7%. The structure is based upon the [(UO2)6O8(OH)2]6+ sheets of uranyl polyhedra of the β-U3O8 anion topology with Pb2+ cations and H2O groups in the interlayer. Billietite and spriggite contain only hexavalent U in the uranyl sheets, whereas the similar sheets in β-U3O8 contain U5+ and U6+, and those in ianthinite U4+ and U6+. Spriggite has the highest Pb:U ratio among the known hydrated Pb uranyl oxyhydroxide minerals.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Composition and I4/m-P42/n phase transition in scapolite solid solutions
- Synthesis and characterization of K2Ca5(SO4)6·H2O, the equivalent of görgeyite, a rare evaporite mineral
- Phase relations in the system Fe-FeSi at 21 GPa
- The speciation of dissolved H2O in dacitic melt
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- Experimental determination of siderite stability and application to Martian Meteorite ALH84001
- Determination of the molar absorption coefficient for the infrared absorption band of CO2in rhyolitic glasses
- Crystallographic properties of the calcium phosphate mineral, brushite, by means of First Principles calculations
- The crystal structure of jonesite, Ba2(K,Na)[Ti2(Si5Al)O18(H2O)](H2O)n: A first example of titanosilicate with porous double layers
- Crystal-chemistry of talc: A near infrared (NIR) spectroscopy study
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- Sieve-textured plagioclase in dacitic magma: Interference imaging results
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- The structure of metahohmannite, Fe3+2[O(SO4)2]⋅4H2O, by in situ synchrotron powder diffraction
- High-pressure synchrotron X-ray diffraction study of spessartine and uvarovite: A comparison between different equation of state models
- Quantum calculations of the electronic structure and NMR quadrupolar interaction parameters for tugtupite
- Identification of pyrite valence band contributions using synchrotron-excited X-ray photoelectron spectroscopy
- Micro-Raman studies of gypsum in the temperature range between 9 K and 373 K
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- Structural and chemical response to varying [4]B content in zoned Fe-bearing olenite from Koralpe, Austria
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