Gauthierite, KPb[(UO2)(7)O-5(OH)(7)]center dot 8H(2)O, a new uranyl-oxide hydroxy-hydrate mineral from Shinkolobwe with a novel uranyl-anion sheet-topology

Warning

This publication doesn't include Faculty of Sports Studies. It includes Faculty of Science. Official publication website can be found on muni.cz.
Authors

OLDS Travis PLÁŠIL Jakub KAMPF Antony ŠKODA Radek BURNS Peter ČEJKA Jiří BOURGOIN Vincent BOULLIARD Jean-Claude

Year of publication 2017
Type Article in Periodical
Magazine / Source European Journal of Mineralogy
MU Faculty or unit

Faculty of Science

Citation
Doi http://dx.doi.org/10.1127/ejm/2017/0029-2586
Keywords gauthierite; new mineral; uranyl-oxide hydroxy-hydrate; crystal structure; topology; oxidation zone; Shinkolobwe
Description Gauthierite, KPb[(UO2)(7)O-5(OH)(7)]center dot 8H(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(1)/c, with a = 29.844(2) angstrom, b = 14.5368(8) angstrom, c = 14.0406(7) angstrom, beta = 103.708(6)degrees, V = 5917.8(6) angstrom(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 similar to 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(3). Optically, gauthierite is biaxial (-), with alpha = 1.780(5), beta = 1.815(5), gamma = 1.825(5) (white light), 2V(meas.) = 58(1)degrees; dispersion is extreme (r >>nu). The optical orientation is X = b, Y approximate to a*, Z approximate to 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 approximate to Z. Electron microprobe analyses (average of 9) provided: K2O 1.29, PbO 7.17, UO3 82.10, H2O 8.78 (structure), total 99.34 wt.%. The empirical formula (based on 34 O a.p.f.u.) is: K0.67Pb0.78U7O34H23.77. The ideal formula is KPb[(UO2)(7)O-5(OH)(7)](H2O)(8), which requires K2O 1.90, PbO 9.00, UO3 80.74, H2O 8.35, total 100 wt.%. Raman and infrared spectral data confirm the presence of UO22+, OH- and molecular H2O. The eight strongest powder X-ray diffraction lines are [d(obs) in angstrom (hkl) I-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>3 sigma(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-4(UD)(6). Adjacent sheets are linked through K+ and Pb2+ cations (the lone 6s(2) pair on Pb atoms is stereoactive).
Related projects:

You are running an old browser version. We recommend updating your browser to its latest version.

More info