Revision of the crystal structure and chemical formula of weeksite, K2(UO 2) 2(Si 5O 13)̇4H 2O

Karla Fejfarová, Jakub Plášil, Hexiong Yang, Jirí Cejka, Michal Dušek, Robert T. Downs, Madison C. Barkley, Radek Škoda

Research output: Contribution to journalArticle

5 Scopus citations

Abstract

The previously published structure determination of weeksite from the Anderson mine, Arizona, U.S.A., suggested that it is orthorhombic, Cmmb, with a = 14.209(2), b = 14.248(2), c = 35.869(4) Å, and V = 7262(2) Å3, and an ideal chemical formula (K,Ba)1-2(UO 2) 2(Si 5O 13)̇H 2O. Using single-crystal X-ray diffraction, electron microprobe analysis, and thermal analysis, we reexamined weeksite from the same locality. Our results demonstrate that weeksite is monoclinic, with the space group C2/m and unit-cell parameters a = 14.1957(4), b = 14.2291(5), c = 9.6305(3) Å, b = 111.578(3)°, V = 1808.96(10) Å3, and an ideal formula K2(UO 2) 2(Si 5O 13)̇4H 2O. The previously reported orthorhombic unit cell is shown to result from twinning of the monoclinic cell. The structure refinement yielded R1 = 2.84% for 1632 observed reflections [Iobs > 3s(I)] and 5.42% for all 2379 reflections. The total H 2O content derived from the structure refinement agrees well with that from the thermal analysis. Although the general topology of our structure resembles that reported previously, all Si sites in our structure are fully occupied, in contrast to the previous structure determination, which includes four partially occupied SiO 4 tetrahedra. From our structure data on weeksite, it appears evident that the orthorhombic cell of the newly discovered weeksite-type mineral coutinhoite, ThxB1-2x(UO 2) 2Si 5O 13̇3H 2O, needs to be reevaluated

Original languageEnglish (US)
Pages (from-to)750-754
Number of pages5
JournalAmerican Mineralogist
Volume97
Issue number4
DOIs
StatePublished - Apr 1 2012

Keywords

  • Crystal structure
  • Open framework
  • Uranyl silicate
  • Weeksite
  • X-ray diffraction

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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    Fejfarová, K., Plášil, J., Yang, H., Cejka, J., Dušek, M., Downs, R. T., Barkley, M. C., & Škoda, R. (2012). Revision of the crystal structure and chemical formula of weeksite, K2(UO 2) 2(Si 5O 13)̇4H 2O. American Mineralogist, 97(4), 750-754. https://doi.org/10.2138/am.2012.4025