Improved calibrations for Raman-spectroscopic determinations of CO2 in cordierite using three excitation wavelengths (488, 515 and 633 nm)
Haefeker, Udo; Kaindl, Reinhard; Tropper, Peter
European Journal of Mineralogy Volume 25 Number 5 (2014), p. 745 - 753
published: Jan 3, 2014
Open Access (paper can be downloaded for free)
Ten natural cordierite single crystals with X Fe in the range 0.044?0.76 and 0.12 to 1.97 wt% CO2 were investigated with Raman microspectroscopy using three different wavelengths. Improved calibration diagrams for CO2 determinations in single crystals and thin sections for the 488, 515 and 633 nm laser excitation wavelengths show significantly lower standard deviations for CO2 determinations (±0.04 to 0.07 wt%) compared to an earlier study done solely at 633 nm. The diagrams are based on the linear relationship between CO2 in wt.% and the ratios of the Raman peak of CO2 to two Si-O-stretching vibrations. The consideration of orientation dependencies and the improvement of background corrections and spectra fitting procedures also contributed to the significantly higher precision. Because Fe-incorporation in cordierite leads to structural changes that result in Raman peak shifts and peak broadening, including peaks considered in this investigation, a correction was introduced for precise CO2 determination on Fe-bearing samples. This improved CO2 determination method was then applied on a 2D spatial scale to two cordierite grains in a thin section of a granulite-facies metapelite from Kösseldorf in the Sauwald area (southern Bohemian Massif, Upper Austria), which yielded CO2 contents of 0.27?0.31 ±0.07 wt%.