Crystal structure of the uranyl-molybdate mineral calcurmolite Ca[(UO2)3(MoO4)2(OH)4](H2O)˜5.0: insights from a precession electron-diffraction tomography study

IF 1.1 4区地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS

Journal of Geosciences Pub Date : 2020-04-12 DOI:10.3190/jgeosci.297

G. Steciuk, R. Škoda, J. Rohlíček, J. Plášil

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引用次数: 4

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(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 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).

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铀酰钼酸盐钙镁石Ca[(UO2)3(MoO4)2(OH)4](H2O)≈5.0的晶体结构:来自进动电子衍射层析研究的见解

Calcurmolite是一种罕见的浅生铀矿物，形成于铀岩和深生钼矿物的蚀变-水化风化过程中；由于缺乏适用于常规结构分析的晶体材料，其结构仍未解决。在这里，单晶进动电子衍射层析成像显示了待调制的钙铬铁矿（Rabejac，France）结构；它是三斜晶系，在超空间群P1（α00）0中结晶，a=3.938Å，b=11.26Å，c=14.195Å，α=84.4°，β=112.5°，γ=133.95°，调制矢量q=0.4 a*。由于衍射数据质量差，尽管最终结果是合理的，但只进行了运动学改进：观察到的3953/1742次/所有反射的Robs/Rall=0.3825/0.3834。钙铬铁矿的结构是基于具有鲍矿拓扑结构（U:Mo比率=1.5）的无限铀酰-钼酸盐片和具有间隙H2O的6配位Ca2+阳离子的夹层（配体是顶端的铀酰O原子和分子H2O）。相邻的薄片通过Ca–O以及氢键连接。基于超晶胞5a×b×c中的假定占有率，结构公式为Ca[（UO2）3（MoO4）2（OH）4]（H2O）~5.0（对于Z=4）。

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来源期刊

Journal of Geosciences GEOSCIENCES, MULTIDISCIPLINARY-MINERALOGY

CiteScore

2.30

自引率

7.10%

发文量

审稿时长

>12 weeks

期刊介绍： The Journal of Geosciences is an international peer-reviewed journal published by the Czech Geological Society with support from the Czech Geological Survey. It accepts high-quality original research or review papers dealing with all aspects of the nature and origin of igneous and metamorphic rocks. The Journal focuses, mainly but not exclusively, on: -Process-oriented regional studies of igneous and metamorphic complexes- Research in structural geology and tectonics- Igneous and metamorphic petrology- Mineral chemistry and mineralogy- Major- and trace-element geochemistry, isotope geochemistry- Dating igneous activity and metamorphic events- Experimental petrology and mineralogy- Theoretical models of igneous and metamorphic processes- Mineralizing processes and mineral deposits. All the papers are written in English, even though they may be accompanied by an additional Czech abstract. Each contribution is a subject to peer review by at least two independent reviewers, typically at least one from abroad. The Journal appears 2 to 4 times a year. Formally it is divided in annual volumes, each of them including 4 issues.