A vibrational spectroscopic study of the phosphate mineral cyrilovite Na(Fe3+)(3)(PO4)(2)(OH)(4)center dot 2(H2O) and in comparison with wardite

Vibrational spectroscopy enables subtle details of the molecular structure of cyrilovite to be determined. Single crystals of a pure phase from a Brazilian pegmatite were used. Cyrilovite is the Fe3+ member of the wardite group. The infrared and Raman spectroscopy were applied to compare the structure of cyrilovite with that of wardite. The Raman spectrum of cyrilovite in the 800-1400 cm(-1) spectral range shows two intense bands at 992 and 1055 cm(-1) assigned to the nu(1) PO43- symmetric stretching vibrations. A series of low intensity bands at 1105, 1136, 1177 and 1184 cm(-1) are assigned to the nu(3) PO43- antisymmetric stretching modes. The infrared spectrum of cyrilovite in the 500-1300 cm(-1) shows much greater complexity than the Raman spectrum. Strong infrared bands are found at 970 and 1007 cm(-1) and are attributed to the nu(1) PO43- symmetric stretching mode. Raman bands are observed at 612 and 631 cm(-1) and are assigned to the nu(4) out of plane bending modes of the PO43- unit. In the 2600-3800 cm(-1) spectral range, intense Raman bands for cyrilovite are found at 3328 and 3452 cm(-1) with a broad shoulder at 3194 cm(-1) and are assigned to OH stretching vibrations. Sharp infrared bands are observed at 3485 and 3538 cm(-1). Raman spectroscopy complimented with infrared spectroscopy has enabled the structure of cyrilovite to be ascertained and compared with that of wardite. (c) 2013 Elsevier B.V. All rights reserved.