Any of a group of hard glassy minerals (silicates of various metals) used as gemstones and as an abrasive.
Group of silicate minerals with the formula X3Y2(SiO4)3 , when X is calcium, magnesium, iron, or manganese, and Y is iron, aluminum, or chromium. Garnets are used as semiprecious gems (usually pink to deep red) and as abrasives.
They occur in metamorphic rocks such as gneiss and schist.