IR calibrations for water determination in olivine, r-GeO2, and SiO2 polymorphs

Mineral-specific IR absorption coefficients were calculated for natural and synthetic olivine, SiO2 polymorphs, and GeO2 with specific isolated OH point defects using quantitative data from independent techniques such as proton-proton scattering, confocal Raman spectroscopy, and secondary ion mass spectrometry. Moreover, we present a routine to detect OH traces in anisotropic minerals using Raman spectroscopy combined with the Comparator Technique''. In case of olivine and the SiO2 system, it turns out that the magnitude of epsilon for one structure is independent of the type of OH point defect and therewith the peak position (quartz epsilon = 89,000 +/- 15,000 1 mol(H2O)(-1) cm(-2)), but it varies as a function of structure (coesite epsilon = 214,000 +/- 14,000 1 mol(H2O)(-1) cm(-2); stishovite epsilon = 485,000 +/- 109,000 1 mol(H2O)(-1) cm(-2)). Evaluation of data from this study confirms that not using mineral-specific IR calibrations for the OH quantification in nominally anhydrous minerals leads to inaccurate estimations of OH concentrations, which constitute the basis for modeling the Earth's deep water cycle.