Abstract
Uranopilite, (UO~2~)~6~(SO~4~)O~2~(OH)~6~(H~2~O)~6~~8~, the composition of which may vary, can be understood as a complex hydrated uranyl oxyhydroxy sulfate. The structure of uranopilite from different locations has been studied by Raman spectroscopy at 298 and 77 K. A single intense band at 1009 cm^−1^ assigned to the ν~1~ (SO~4~)^2−^ symmetric stretching mode shifts to higher wavenumbers at 77 K. Three low‐intensity bands are observed at 1143, 1117 and 1097 cm^−1^. These bands are attributed to the (SO~4~)^2−^ ν~3~ anti‐symmetric stretching modes. Multiple bands provide evidence that the symmetry of the sulfate anion in the uranopilite structure is lowered. Three bands are observed in the region 843 to 816 cm^−1^ in both the 298 and 77 K spectra and are attributed to the ν~1~ symmetric stretching modes of the (UO~2~)^2+^ units. Multiple bands prove the symmetry reduction of the UO~2~ ion. Multiple OH stretching modes prove a complex arrangement of OH groupings and hydrogen bonding in the crystal structure. A series of infrared bands not observed in the Raman spectra are found at 1559, 1540, 1526 and 1511 cm^−1^ attributed to δ UOH bending modes. U‐O bond lengths in uranyl and OH/dotbondO bond lengths are calculated and compared with those from X‐ray single crystal structure analysis. The Raman spectra of uranopilites of different origins show subtle differences, proving that the spectra are origin‐ and sample‐dependent. Hydrogen‐bonding network and its arrangement in the crystal structure play an important role in the origin and stability of uranopilite. Copyright © 2006 John Wiley & Sons, Ltd.