Garnet is a widespread mineral in crustal metamorphic rocks, a primary constituent of the mantle, a detrital mineral in clastic sediments, and an occasional guest in igneous rocks. Garnet occurs in ultramafic to felsic bulk-rock compositions, and its growth and stability span from <300 to 2000 °C and from atmospheric pressure to 25 GPa. More than merely a constituent of these rocks, garnet possesses chemical and physical attributes allowing it to record, and influence, a diverse suite of tectonic, metamorphic, and mantle processes, making it uncommonly useful in geoscientific inquiry. Because of its myriad colors, garnet has been used through the ages in jewelry. More recently, nonsilicate crystals with the garnet structure have been fabricated for sophisticated laser, magnetic, and ion-conducting technologies.