Garnet is the general name given to a group of complex silicate minerals, all with isometric crystal structure and similar properties and chemical composition. The most common garnet minerals are classified into three groups: the aluminum-garnet group, the chromium-garnet group and the iron-garnet group. Worldwide, garnet resources are large and occur in a wide variety of rocks, principally in metamorphic rocks such as gneisses and schists. Garnet also occurs in veins, contact metamorphic rocks, metamorphosed crystalline limestones, pegmatites and serpentinites. In addition, alluvial garnet sands are associated with heavy-mineral sand and gravel deposits in many parts of the world.