Identification and composition of carbonate minerals of the calcite structure by Raman and infrared spectroscopies using portable devices.

ABSTRACT

A portable Raman device with a 532 nm excitation laser and a portable infrared spectrometer with ATR (Attenuated Total Reflection) mode were used to analyse the spectral features associated with the identification and compositional variation of Ca-Mg-Fe-Mn natural carbonate minerals with a calcite structure (calcite, ankerite, dolomite, siderite, rhodochrosite, and magnesite). A systematic study of the variations of the peak positions with various compositional ratios was carried out. Most of the band positions were shifted to lower wavenumbers with increasing ionic radius or atomic mass of the divalent cations but the band of the translational lattice (T) mode in Raman and the symmetric bending (ν4) band in the mid-infrared were the most sensitive. Therefore, the elemental variation of the Ca-Mg-Fe-Mn ratio in this carbonate series can be estimated from Raman and infrared band positions from spectra acquired with portable spectrometers.