The structure of agrinierite: a Sr-containing uranyl oxide hydrate mineral
-
C.L. Cahill
and
P.C. Burns
Abstract
The structure of agrinierite, K2(Ca0.65Sr0.35)[(UO2)3O3(OH)2]2·5H2O, orthorhombic, F2mm, Z = 16, a = 14.094(2), b = 14.127(2), c = 24.106(4) Å, V = 4799.6(1) Å3, was solved by direct methods and refined by full-matrix least-squares techniques to an agreement factor (R) of 6.55% and a goodness- of-fit (S) of 0.851 using 2710 independent observed reflections collected with MoKα X-radiation and a CCD-based detector. This layered material contains four unique U6+ positions, each of which is part of a nearly linear (UO2)2+ uranyl ion. The U6+ cations are further coordinated by five anions occupying the equatorial vertices of pentagonal bipyramids that are capped by the uranyl ion O atoms. The uranyl polyhedra are linked by the sharing of equatorial vertices and edges in a fashion topologically identical to the α-U3O8 sheet found in billietite, protasite, becquerelite, richetite, compreignacite and masuyite. The arrangement of hydroxyl anions within the sheets varies in these minerals; that of agrinierite is identical to protasite. The cations (Ca, Sr, and K) and H2O reside in the interlayer region of the structure. The inclusion of Sr in the structure of agrinierite suggests that the release of radioactive 90Sr may be impacted by incorporation into this phase if it forms in a geological repository for nuclear waste.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Measurement of crystal size distributions
- Pressure dependence of the solubility of Ar and Kr in melts of the system SiO2-NaAlSi2O6
- Solubility behavior of water in haploandesitic melts at high pressure and high temperature
- Proton-containing defects at forsterite {010} tilt grain boundaries and stepped surfaces
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- Aluminium coordination in tektites: A XANES study
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- The tremolite-actinolite-ferro–actinolite series: Systematic relationships among cell parameters, composition, optical properties, and habit, and evidence of discontinuities
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- Cordierite II: The role of CO2 and H2O
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- The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry
- The crystal structure of pararobertsite and its relationship to mitridatite
- Description and crystal structure of cabalzarite Ca(Mg,Al,Fe)2(AsO4)2(H2O,OH)2, a new mineral of the tsumcorite group
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