A vibrational spectroscopic study of the anhydrous phosphate mineral sidorenkite Na3Mn(PO4)(CO3)

Sidorenkite is a very rare low-temperature hydrothermal mineral, formed very late in the crystallization of hyperagpaitic pegmatites in a differentiated alkalic massif (Mt. Alluaiv, Kola Peninsula, Russia). Sidorenkite Na3Mn(PO4)(CO3) is a phosphate-carbonate of sodium and manganese. Such a formula with two oxyanions lends itself to vibrational spectroscopy. The sharp Raman band at 959 cm(-1) and 1012 cm-1 are assigned to the PO43- stretching modes, whilst the Raman bands at 1044 cm(-1) and 1074 cm(-1) are attributed to the CO32- stretching modes. It is noted that no Raman bands at around 800 cm(-1) for sidorenkite were observed. The infrared spectrum of sidorenkite shows a quite intense band at 868 cm(-1) with other resolved component bands at 850 and 862 cm(-1). These bands are ascribed to the CO32- out-of-plane bend (v(2)) bending mode. The series of Raman bands at 622, 635, 645 and 704 cm(-1) are assigned to the v(4) phosphate bending modes. The observation of multiple bands supports the concept of a reduction in symmetry of the carbonate anion from D-3h or even C-2v. (C) 2014 Elsevier B.V. All rights reserved.