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Gauthierite, KPb[(UO (super 2) ) (sub 7) O (sub 5) (OH) (sub 7) ].8H (sub 2) O, a new uranyl-oxide hydroxy-hydrate mineral from Shinkolobwe with a novel uranyl-anion sheet-topology

Travis A. Olds, Jakub Plasil, Anthony R. Kampf, Radek Skoda, Peter C. Burns, Jiri Cejka, Vincent Bourgoin and Jean-Claude Boulliard
Gauthierite, KPb[(UO (super 2) ) (sub 7) O (sub 5) (OH) (sub 7) ].8H (sub 2) O, a new uranyl-oxide hydroxy-hydrate mineral from Shinkolobwe with a novel uranyl-anion sheet-topology
European Journal of Mineralogy (October 2016) 29 (1): 129-141

Abstract

Gauthierite, KPb[(UO (sub 2) ) (sub 7) O (sub 5) (OH) (sub 7) ].8H (sub 2) O, is a new uranyl-oxide hydroxy-hydrate mineral from the Shinkolobwe Mine, Democratic Republic of Congo, Africa. It occurs on a matrix of uraninite-bearing quartz gangue associated with soddyite and a minor metazeunerite-metatorbernite series mineral. It is a product of oxidation-hydration weathering of uraninite. Gauthierite is monoclinic, P2 (sub 1) /c, with a = 29.844(2) A, b = 14.5368(8) A, c = 14.0406(7) A, beta = 103.708(6) degrees , V = 5917.8(6) A (super 3) and Z = 8. Prismatic crystals have pronounced lengthwise striations and reach about 1 mm in length. Gauthierite is yellowish orange with a light orange streak and vitreous lustre. The Mohs hardness is approximately 3 to 4. It is brittle with an uneven fracture and perfect cleavage on {0 1 0}. The calculated density based on the empirical formula is 5.437 g/cm (super 3) Optically, gauthierite is biaxial (-), with alpha = 1.780(5), beta = 1.815(5), gamma = 1.825(5) (white light), 2V (sub meas) = 58(1) degrees ; dispersion is extreme (r >> v). The optical orientation is X = b, Y nearly equal a*, Z nearly equal c (or X = b, Y^a = 14 degrees in obtuse beta ); it is pleochroic with X very pale yellow, Y and Z orange-yellow; X << Y nearly equal Z Electron microprobe analyses (average of 9) provided: K (sub 2) O 1.29, PbO 7.17, UO (sub 3) 82.10, H (sub 2) O 8.78 (structure), total 99.34 wt.%. The empirical formula (based on 34 O a.p.f.u.) is: K (sub 0.67) Pb (sub 0.78) U (sub 7) O (sub 34) H (sub 23.77) . The ideal formula is KPb[(UO (sub 2) ) (sub 7) O (sub 5) (OH) (sub 7) ](H (sub 2) O) (sub 8) , which requires K (sub 2) O 1.90, PbO 9.00, UO (sub 3) 80.74, H (sub 2) O 8.35, total 100 wt.%. Raman and infrared spectral data confirm the presence of UO (sub 2) (super 2+) , OH (super -) and molecular H (sub 2) O. The eight strongest powder X-ray diffraction lines are [d (sub obs) in A (hkl) I (sub rel) ]: 7.28 (020,400) 49, 3.566 (040, -802, -204) 67, 3.192 (622, -224) 100, 2.541 (-842, -244) 18, 2.043 (406) 14, 2.001 (662, -264, 14.2.0) 23, 1.962 (426, -146) 14, and 1.783 (12.0.4, -10.4.6) 17. The crystal structure of gauthierite (R = 0.0567 for 6997 reflections with [I > 3sigma (I)]) contains uranyl-(hydroxo)-oxide sheets with a novel topology that is similar to that of vandendriesscheite, but with a unique chain sequence UDPDPDUPUP, P (sub 4) (UD) (sub 6) . Adjacent sheets are linked through K (super +) and Pb (super 2+) cations (the lone 6s (super 2) pair on Pb atoms is stereoactive).


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 29
Serial Issue: 1
Title: Gauthierite, KPb[(UO (super 2) ) (sub 7) O (sub 5) (OH) (sub 7) ].8H (sub 2) O, a new uranyl-oxide hydroxy-hydrate mineral from Shinkolobwe with a novel uranyl-anion sheet-topology
Affiliation: University of Notre Dame, Department of Civil and Environmental Engineering and Earth Sciences, Notre Dame, IN, United States
Pages: 129-141
Published: 20161017
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 49
Accession Number: 2016-094593
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
N11°02'55" - N11°02'55", E26°33'03" - E26°33'03"
Secondary Affiliation: Czech Academy of Sciences, Institute of Physics, CZE, Czech RepublicNatural History Museum of Los Angeles County, USA, United StatesMasaryk University, CZE, Czech RepublicNational Museum, CZE, Czech RepublicUniversite Pierre et Marie Curie, FRA, France
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201646
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