A Raman spectroscopic study of the natural carbonophosphates Na₃<i>M</i>CO₃PO₄ (<i>M</i> is Mn, Fe, and Mg)

Abstract

Abstract. Raman spectra of three natural carbonophosphates (sidorenkite, bonshtedtite, and bradleyite) with the general formula Na3MCO3PO4 (M is Mn, Fe, and Mg) were studied and compared. These spectra showed from 21 to 24 vibrational bands, of which the two most intense (964±5 and 1074±3 cm−1) correspond to the υ1(P–O) and υ1(C–O) modes. These two bands split into doublet peaks due to the occurrence of isomorphic impurities. It was found that the crystallographic orientation of the sample influences the intensity of most bands. Most bands assigned to the same vibrations showed a regular shift (the smallest in sidorenkite spectra, an intermediate in bonshtedtite, and the largest in bradleyite). We propose an algorithm that allows for diagnostics of carbonophosphates in inclusions by their Raman spectra, providing a reliable result even in the absence of energy-dispersive X-ray spectroscopy (EDX) data.