Characterization of inorganic and biogenic magnesian calcites by Fourier Transform infrared spectroscopy

The effect of cationic substitution on the mid-infrared absorption spectra of synthetic, and natural inorganic and biogenic MgCO 3-CaCO 3 solid solutions (Mg calcites; space group R3̄c; 0–23 mol% MgCO 3) is investigated, and the results are compared to disordered proto-dolomite (Ca 0.5Mg 0.5CO 3; space group R3̄c), ordered dolomite (Ca 0.5Mg 0.5CO 3; space group R3̄), huntite (Ca 0.25Mg 0.75CO 3; space group R32), and magnesite (MgCO 3; space group R3̄c). The measurements show that significant frequency shifts of the vibrational bands of the carbonate ion group occur as a function of chemical composition. The Mg 2+ content of all Mg calcites correlates linearly with the position of the sharp v4 mode according to: v4 (cm −1) = 39.40 X Mg + 712.20 ( r = 0.97).