Publication details
Crystal structure of the uranyl-oxide mineral rameauite
| Authors | |
|---|---|
| Year of publication | 2016 |
| Type | Article in Periodical |
| Magazine / Source | European Journal of Mineralogy |
| MU Faculty or unit | |
| Citation | |
| Web | Full Text |
| Doi | http://dx.doi.org/10.1127/ejm/2016/0028-2568 |
| Keywords | rameauite; uranyl-oxide hydroxy-hydrate; crystal structure; Raman spectrum |
| Description | Rameauite is a rare supergene uranyl-oxide hydroxy-hydrate mineral that forms during hydration-oxidation weathering of uraninite. On the basis of single-crystal X-ray diffraction data collected on a microfocus source, rameauite is monoclinic, space group Cc, with a = 13.9458(19), b = 14.3105(19), c = 13.8959(18) angstrom, beta = 118.477(14)degrees, V = 2437.7(6) angstrom(3) and Z = 4, with D-calc = 5.467 g cm(-3). The structure of rameauite (R = 0.060 for 1698 unique observed reflections) contains sheets of the beta-U3O8 topology, with both UO6 and UO7 bipyramids, which is similar to the sheets found in spriggite, ianthinite and wyartite. The sheets alternate with the interlayer, which contains K+, Ca2+ and H2O molecules. Interstitial cations are linked into infinite chains that extend along [10-1]. Adjacent sheets are linked through K-O, Ca-O and H-bonds. The structural formula of rameauite is K2Ca((H2O)-O-[3]) 1((H2O)-O-[5])(4)[(UO2) O-6(6)(OH)(4)](H-2([4]) O)(1). The empirical formula obtained from the average of eight electron-microprobe analyses is (on the basis of 6 U p.f.u.) K-1.87(Ca1.10Sr0.04)(Sigma 1.14)[(UO2)(6)O-6(OH)(4.15)]center dot 6H(2)O. The Raman spectrum is dominated by U-O and O-H vibrations. A discussion of related uranyl- oxide minerals is given. |