Most minerals of Earth's upper mantle contain small amounts of hydrogen, structurally bound as hydroxyl (OH). The OH concentration in each mineral species is variable, in some cases reflecting the geological environment of mineral formation. Of the major mantle minerals, pyroxenes are the most hydrous, typically containing ∼200 to 500 parts per million H ₂ O by weight, and probably dominate the water budget and hydrogen geochemistry of mantle rocks that do not contain a hydrous phase. Garnets and olivines commonly contain ∼1 to 50 parts per million. Nominally anhydrous minerals constitute a significant reservoir for mantle hydrogen, possibly accommodating all water in the depleted mantle and providing a possible mechanism to recycle water from Earth's surface into the deep mantle.

Using IR absorption data from polarized measurements on single-crystal minerals with stoichiometric water contents (in the form of H ₂ O or OH groups in the structure), a linear calibration curve (r ² nearly equal 0.98) for water in minerals is established in the form: epsilon _i , (the integrated molar absorption coefficient in units of cm (super -2) per mol H ₂ O/L) = 246.6(3753 - upsilon ) (upsilon = the mean wavenumber of the OH stretching band [in cm (super -1) ]). The investigated minerals include hydrogrossular, analcime, hemimorphite and its dehydrated phase, lawsonite, goethite, diaspore, manganite, mozartite, and pectolite. The influence of hydrogen bonding, leading to increased absorption values with lower OH stretching band energies, is confirmed. It is further shown that only the use of integrated absorbance values (band areas) results in a linear correlation with water content, whereas linear absorption data (peak heights) are not correlated. The calibration agrees with previously published quantitative IR data on staurolite and trace H in pyroxenes. It is also close to the frequently used trend of Paterson (1982). However, some of the previous calibrations of trace H in nominally anhydrous minerals, e.g., kyanite and pyrope, differ appreciably from the correlation derived from stoichiometrically hydrous minerals.