The absorption features result from vibrations of the C-O bonds in the carbonate anion. The subtle shifts in absorption band positions arise from the slight variations in the crystal lattice between each type of carbonate. These variations result from a different cation being associated with each carbonate (e.g., Ca in calcite, Mg in magnesite). Vertical lines are placed through the emissivity minima of calcite for comparison to the other carbonate absorption band positions.

This figure is from Lane, M.D. and P.R. Christensen,Thermal infrared emission spectroscopy of anhydrous carbonates, J. Geophys. Res., 102, 25581-25592, 1997.

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