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Title: Wyartite: Crystallographic evidence for the first pentavalent-uranium mineral

Abstract

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 withmore » a U{sup 6+}{phi}{sub 7} polyhedron. Structural units are linked together through hydrogen bonds only.« less

Authors:
 [1];  [2]
  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.
Publication Date:
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
697153
Resource Type:
Journal Article
Journal Name:
American Mineralogist
Additional Journal Information:
Journal Volume: 84; Journal Issue: 9; Other Information: PBD: Sep 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; URANIUM MINERALS; CRYSTAL STRUCTURE; VALENCE; PETROGENESIS; URANINITES; DEMOCRATIC REPUBLIC OF THE CONGO

Citation Formats

Burns, P.C., and Finch, R.J. Wyartite: Crystallographic evidence for the first pentavalent-uranium mineral. United States: N. p., 1999. Web. doi:10.2138/am-1999-0926.
Burns, P.C., & Finch, R.J. Wyartite: Crystallographic evidence for the first pentavalent-uranium mineral. United States. doi:10.2138/am-1999-0926.
Burns, P.C., and Finch, R.J. Wed . "Wyartite: Crystallographic evidence for the first pentavalent-uranium mineral". United States. doi:10.2138/am-1999-0926.
@article{osti_697153,
title = {Wyartite: Crystallographic evidence for the first pentavalent-uranium mineral},
author = {Burns, P.C. and Finch, R.J.},
abstractNote = {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.},
doi = {10.2138/am-1999-0926},
journal = {American Mineralogist},
number = 9,
volume = 84,
place = {United States},
year = {1999},
month = {9}
}