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  • Title: A vibrational spectroscopic study of the phosphate mineral cyrilovite Na(Fe3+)3(PO4)2(OH)4·2(H2O) and in comparison with wardite.
    Author: Frost RL, Xi Y, Scholz R.
    Journal: Spectrochim Acta A Mol Biomol Spectrosc; 2013 May; 108():244-50. PubMed ID: 23501935.
    Abstract:
    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 Fe(3+) 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 ν1PO4(3-) symmetric stretching vibrations. A series of low intensity bands at 1105, 1136, 1177 and 1184 cm(-1) are assigned to the ν3PO4(3-) 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 ν1PO4(3-) symmetric stretching mode. Raman bands are observed at 612 and 631 cm(-1) and are assigned to the ν4 out of plane bending modes of the PO4(3-) 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.
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