No site-specific infrared absorption coefficients for OH-defects in pure enstatite

Single crystals of pure Mg (sub 2) Si (sub 2) O (sub 6) 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.