Wyartite: Crystallographic evidence for the first pentavalent-uranium mineral

Journal Article · Wed Sep 01 04:00:00 EDT 1999 · American Mineralogist

DOI:https://doi.org/10.2138/am-1999-0926· OSTI ID:697153

Burns, P C ^[1]; Finch, R J ^[2]

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1. Univ. of Notre Dame, IN (United States). Dept. of Civil Engineering and Geological Sciences
2. Argonne National Lab., IL (United States). Chemical Technology Div.

Determination of the structure of wyartite provides the first evidence for a pentavalent-U mineral. The structure of wyartite, CaU{sup 5+}(UO{sub 2}){sub 2}(CO{sub 3})O{sub 4}(OH)(H{sub 2}O), was solved by direct methods and refined to an agreement index (R) of 4.9% for 2309 unique reflections collected using MoK{alpha}X-radiation and a CCD-based detector. The structure contains three unique U positions; two contain U{sup 6+} and involve uranyl ions with typical pentagonal-bipyramidal coordination. Seven anions coordinate the other U position, but there is no uranyl ion present. The polyhedral geometry, the bond-valence sum incident at this U site, and electroneutrality requirements, all indicate that this site contains U{sup 5+}. The U{phi}{sub 7} ({phi}: O, OH, H{sub 2}O) polyhedra share edges and corners to form a unique sheet in which a CO{sub 3} group shares an edge with the U{sup 5+}{phi}{sub 7} polyhedron. The structure contains one Ca site coordinated by seven anions. The Ca atom and its associated H{sub 2}O groups occupy interlayer sites, along with two H{sub 2}O groups that are held in the structure by H bonds only. The Ca{phi}{sub 7} polyhedron is linked to one adjacent sheet by sharing an edge with the CO{sub 3} group and an O atom with a U{sup 6+}{phi}{sub 7} polyhedron. Structural units are linked together through hydrogen bonds only.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• OSTI ID: 697153
• Journal Information: American Mineralogist, Journal Name: American Mineralogist Journal Issue: 9 Vol. 84; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CRYSTAL STRUCTURE
DEMOCRATIC REPUBLIC OF THE CONGO
PETROGENESIS
URANINITES
URANIUM MINERALS
VALENCE