An infrared spectroscopic study in parts of the quaternary system CaCO3-MnCO3-MgCO3-FeCO3.

The mid-infrared spectrum of calcite- and dolomite-structured carbonates shows three active internal modes: 2, 3, and 4, where the sharp 2- and 4-bands seem to be best suited to distinguish between various minerals. 2 and 4 arise from the out-of-plane and in-plane bending mode of the carbonate ion, respectively.

The infrared spectroscopic measurements of synthetic and natural carbonate samples show that significant frequency shifts in the 2 and 4 vibrational bands occur in the investigated binary systems as a function of the chemical composition. These shifts are due to cationic substitution, reflecting the different ionic radii and masses of the end-members. Based on these results, tentative models for the variations of 2 and 4 in the ternary systems are presented. Plots of 2 versus 4 enable the determination of the chemical composition of carbonate specimens.