These studies rely heavily upon spectroscopic methods of analysis because they can determine both the chemical species present and, with proper calibration, the amount of hydrogen present. Both water molecules and hydroxide groups are found in a variety of minerals. Initial studies focused on water in quartz because of its weakening effect upon the mechanical strength of this mineral. We showed that while OH groups have no effect upon the strength of quartz, the amount of water present as clusters of a few water molecules was directly associated with mechanical weakening. Hydroxide groups have subsequently been found in plagioclase feldspars, garnets, sillimanite and other aluminosilicates, olivines, clinopyroxenes, orthopyroxenes, quartz, rutile and zircon.
Water molecules occur in nepheline, potassium feldspar, cordierite and other ring silicates.
These molecules and ions are structurally bound in the mineral in definite sites with distinct orientations. Consequently, we are particularly interested in characterizing hydrous components in garnets. When present at low concentration, infrared and nuclear magnetic resonance spectroscopic data suggest a variety of other incorporation mechanisms. In some silicate minerals, the incorporation of hydrogen is coupled with other light elements such as boron. Much of our interest in hydrous components has focused on the volatile reservoirs and inventories in the upper mantle.