IR spectroscopic characterization of OH defects in mineral phases

Infrared spectroscopy provides information on structural sites, hydrogen bond lengths, and concentrations of trace amounts of hydrogen in nominally anhydrous minerals. OH defects in olivine are predominately associated with vacant Si and Mg/Fe sites. However, even trace inclusions of hydrous minerals like serpentine and talc have been detected. In pyroxenes OH defects are also most likely associated with cation vacancies. Garnets of the grossular series contain abundant water in the form of (OH)(4) "hydrogarnet" defects. Other garnets show a wide variety of additional OH defects that can only scarcely be assigned. MgSiO3 perovskite, a high-pressure phase of the Earth's mantle, contains only minor amounts of OH defects related to Mg vacancies. Well-crystallized zircons contain only trace amounts of OH defects, whereas large amounts of hydrogen (OH and H2O) have been observed in radiation-damaged, metamict zircon. In rutile-type minerals, OH defects compensate for trivalent cations.