Studies of OH in nominally anhydrous minerals

Hydrous components in nominally anhydrous minerals have been the object of increasing study for the past three decades. OH ions and, less commonly, H₂O molecules are found in many anhydrous minerals at concentrations ranging from ppms to tenth's of a percent by weight. Infrared spectroscopy remains the preferred method to characterize these components because of its sensitivity to chemical species, crystallographic orientation and analytical concentration. Improved calibration of the infrared measurements provides a quantitative understanding of the importance of the global hydrogen reservoir contained in the “anhydrous” phases. New and revised values for the amount of H₂O in anhydrous minerals are summarized.