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- Title
Crystal structure of the uranyl-molybdate mineral calcurmolite Ca[(UO<sub>2</sub>)<sub>3</sub>(MoO<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>](H<sub>2</sub>O)<sub>~5.0</sub>: insights from a precession electron-diffraction tomography study.
- Authors
STECIUK, Gwladys; ŠKODA, Radek; ROHLÍČEK, Jan; PLÁŠIL, Jakub
- Abstract
Calcurmolite is a rare supergene U mineral formed during the alteration-hydration weathering of uraninite and hypogene Mo minerals; its structure has remained unsolved owing to a lack of crystal material suitable for conventional structure analysis. Here, single-crystal precession electron-diffraction tomography shows the calcurmolite (Rabejac, France) structure to be modulated; it is triclinic, crystallizing in the super-space group P1(a00)0, with a = 3.938 Å, b = 11.26 Å, c = 14.195 Å, α = 84.4°, ß = 112.5°, γ = 133.95° and has a modulation vector q = 0.4 a*. Due to the poor quality of diffraction data, only a kinematical refinement was undertaken, although final results were reasonable: Robs/Rall = 0.3825/0.3834 for 3953/17442 observed/all reflections. The structure of calcurmolite is based upon the infinite uranyl-molybdate sheets with baumoite topology (U : Mo ratio = 1.5) and an interlayer of 6-coordinated Ca2+ cations with interstitial H2O (ligands are apical uranyl O atoms and molecular H2O). Adjacent sheets are linked via Ca-O, as well as H-bonds. The structure formula, based on assumed occupancies in the supercell 5a × b × c, is Ca[(UO2)3 (MoO4)2(OH)4](H2O)~5.0 (for Z = 4).
- Subjects
CRYSTAL structure; MOLYBDENUM; TOMOGRAPHY; CHEMICAL weathering; URANIUM; WATER
- Publication
Journal of Geosciences, 2020, Vol 65, Issue 1, p15
- ISSN
1802-6222
- Publication type
Article
- DOI
10.3190/jgeosci.297