• journal_title：Mineralogical Magazine
• Contributor：J. Plášil ; K. Fejfarová ; R. Skála ; R. Škoda ; N. Meisser ; J. Hloušek ; I. Císařová ; M. Dušek ; F. Veselovský ; J. Čejka ; J. Sejkora ; P. Ondruš
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2012.076.3.01
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：76
• issue：3
• firstpage：443
• section：Articles

Two crystals of the uranyl carbonate mineral grimselite, ideally K₃Na[(UO₂)(CO₃)₃](H₂O), from Jáchymov in the Czech Republic were studied by single-crystal X-ray diffraction and electron-probe microanalysis. One crystal has considerably more Na than the ideal chemical composition due to substitution of Na into KO₈ polyhedra; the composition of the other crystal is nearer to ideal, and similar to synthetic grimselite. The presence of Na atoms in KO₈ polyhedra, which are located in channels in the crystal structure, reduces their volume, and as a result the unit-cell volume also decreases. Structure refinement shows that the formula for the sample with the anomalously high Na content is (K_2.43Na_0.57)_Σ3.00Na[(UO₂)(CO₃)₃](H₂O). The unit-cell parameters, refined in space group P6İ2c, are a = 9.2507(1), c = 8.1788(1) Å, V = 606.14(3) ų and Z = 2. The crystal structure was refined to R₁ = 0.0082 and wR₁ = 0.0185 with a GOF = 1.33, based on 626 observed diffraction peaks [I_obs>3σ(I)].