Mauro Cândido Filho

Raman, infrared and near-infrared spectroscopic characterization of the herderite-hydroxylherderite mineral series.

Natural single-crystal specimens of the herderite-hydroxylherderite series from Brazil, with general formula CaBePO4(F,OH), were investigated by electron microprobe, Raman, infrared and near-infrared spectroscopies. The minerals occur as secondary products in granitic pegmatites. Herderite and hydroxylherderite minerals show extensive solid solution formation. The Raman spectra of hydroxylherderite are characterized by bands at around 985 and 998 cm(-1), assigned to ν1 symmetric stretching mode of the HOPO3(3-) and PO4(3-) units. Raman bands at around 1085, 1128 and 1138 cm(-1) are attributed to both the HOP and PO antisymmetric stretching vibrations. The set of Raman bands observed at 563, 568, 577, 598, 616 and 633 cm(-1) are assigned to the ν4 out of plane bending modes of the PO4 and H2PO4 units. The OH Raman stretching vibrations of hydroxylherderite were observed ranging from 3626 cm(-1) to 3609 cm(-1). The infrared stretching vibrations of hydroxylherderites were observed between 3606 cm(-1) and 3599 cm(-1). By using a Libowitzky type function, hydrogen bond distances based upon the OH stretching bands were calculated. Characteristic NIR bands at around 6961 and 7054 cm(-1) were assigned to the first overtone of the fundamental, whilst NIR bands at 10,194 and 10,329 cm(-1) are assigned to the second overtone of the fundamental OH stretching vibration. Insight into the structure of the herderite-hydroxylherderite series is assessed by vibrational spectroscopy.

Infrared and Raman Spectroscopic Characterization of the Phosphate Mineral Leucophosphite K(Fe3+)2(PO4)2(OH) · 2(H2O)

ABSTRACT The phosphate mineral leucophosphite K(Fe2)3+(PO4)2(OH) · 2H2O has been characterized by SEM-EDS, Raman, and infrared spectroscopic measurements. The mineral is predominantly a K and Fe phosphate with some minor substitution of Al in the Fe3+ site. Raman bands at 994 and 1058 cm−1 are assigned to the symmetric stretching modes of and units. The Raman bands at 1104, 1135, and 1177 cm−1 are assigned to the and antisymmetric stretching modes. Raman and infrared spectra in the 2600–3800 cm−1 region show a complex set of overlapping bands, which may be resolved into the component bands. The Raman bands observed at 3325, 3355, and 3456 cm−1 are attributed to water stretching vibrations, and in the infrared spectrum, bands at 3237, 3317, and 3453 cm−1 are assigned to water stretching bands.