Abstract

Single crystals of pure Mg2Si2O6 orthoenstatite synthesized at 25–80 kbar were analysed by secondary ion mass spectrometry (SIMS) and Fourier transform infrared spectroscopy (FTIR) with respect to water. The IR spectra of the crystals exhibited two groups of OH-absorption bands in varying proportions, ascribed to a varying ratio of two different OH-defects. Different strategies for quantification of the water content based on the comparison of the IR spectra and the SIMS data are evaluated. Results suggest that one single mineral-specific absorption coefficient for enstatite is not useful, and that site-specific absorption coefficients (i.e., coefficients specific to each absorption band) are not necessary. Instead, a function for the absorption coefficient dependence on wavelength could be established. This function is similar to previously formulated wavelength-dependent absorption coefficients for nominally anhydrous minerals, hydrous minerals and water-bearing glasses.

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