Crystal structure of the uranyl-molybdate mineral calcurmolite Ca[(UO 2 ) 3 (MoO 4 ) 2 (OH) 4 ](H 2 O) ~5.0 : insights from a precession electron-diffraction tomography study

Journal of Geosciences

article

Gwladys Steciuk¹  Radek Skoda²  Jan Rohlicek¹  Jakub Plasil¹ 

[1] Institute of Physics, Academy of Sciences of the Czech Republic v.v.i;Department of Geological Sciences, Masaryk University

关键词: calcurmolite;    uranyl–molybdate;    crystal structure;    modulation;    baumoite topology;    precession electron diffraction;   

DOI  :  10.3190/jgeosci.297

学科分类：自动化工程

来源: Ceska Geologicka Spolecnost / Czech Geological Society

【 摘 要 】

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 conventionalstructure 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(α00)0, with a = 3.938 Å,b = 11.26 Å, c = 14.195 Å, α = 84.4°, β = 112.5°, γ = 133.95° and has a modulation vector q = 0.4 a*. Due to thepoor 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 infiniteuranyl–molybdate sheets with baumoite topology (U : Mo ratio = 1.5) and an interlayer of 6-coordinated Ca2+ cationswith 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).

【 授权许可】

CC BY