Quantification of Crystal Chemistry of Fe-Mg Carbonates by Raman Microspectroscopy and Near-Infrared Remote Sensing

On Earth, carbonate minerals are widely used as recorders of the geological environments in which they formed. Here, we present a method designed to retrieve the crystal chemistry of Fe-Mg carbonate minerals using infrared remote sensing or Raman spectroscopy. We analyzed a suite of well-characterized Fe-Mg carbonate minerals for which Raman spectra were obtained in two different laboratories, and IR spectra were measured in reflectance and transmission from the visible range to 25-mu m. We built calibration lines for the dependence of fundamental and harmonic vibrational modes position to the Mg# (defined as Mg# = 100 x Mg/(Mg + Fe + Ca + Mn)). These calibrations should enable retrieval of Mg# based on spectroscopic observations with a typical accuracy of 10. We discuss the framework of applicability of these calibrations and apply them to a typical CRISM spectrum of carbonates from the Nilli Fossae region of Mars. Fundamental FeMg carbonate mode position have a linear dependence to Mg# for Fe-Mg carbonate mineral Harmonic bands at 2.3 and 2.5 also have a linear dependence of their position with Mg# for Fe-Mg carbonate minerals We present calibration curves of Mg# versus fundamental and harmonic vibration position than can be used to retrieve crystal chemistry