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Raman spectroscopy of phosphates of the variscite mineral group

By Ray L. Frost, Matt L. Weier, Kristy L. Erickson, Onuma Carmody and Stuart Mills

Abstract

Raman spectra of phosphates of the variscite mineral group, namely strengite, variscite, metavariscite and phosphosiderite, were obtained at 298 and 77 K using a thermal stage and complemented with selected infrared data using a diamond attenuated total reflection cell. Multiple phosphate stretching bands are observed. Bands for strengite at 1006, 1012 and 1026 cm-1 at 298 K and at 997, 1006, 1014 and 1027 cm-1 at 77 K are observed. Variscite is characterized by PO stretching vibrations at 1023, 1005 and 938 cm-1 and phosphosiderite by bands at 1009 and 993 cm-1. These minerals are readily identified by their Raman spectrum both in the PO stretching region and in the low-wavenumber region. Multiple bands attributed to the bending modes of PO4 are identified for each of the minerals. A model is proposed involving non-hydrogen-bonded PO4 and strongly hydrogen-bonded PO4 units together with [Al or Fe(OH)2]+ ·(H2PO4)2--type species. Raman spectroscopy shows that at the molecular level multiple species of phosphate anions exist for the variscite phosphate minerals

Publisher: John Wiley and Sons
Year: 2004
DOI identifier: 10.1002/jrs.1251
OAI identifier: oai:eprints.qut.edu.au:22119

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