Where Is Garnet Most Commonly Found?

Metamorphic Rocks

• Metamorphic rocks come from putting pre-existing rocks under conditions of high temperature, high pressure or both. The minerals within the rock metamorphose into new ones that are more stable for those conditions. For silicate-based rocks like granite or shale that turn to schist and gneiss, these minerals include garnet.

The Mineral Garnet

• Garnet is usually red but can also be brown, green, yellow, white or black. It tends to form as dodecahedrons or trapezohedrons. Chemically, its formula is A3B2(SiO4)3, where A is either Ca, Mg, Fe2+ or Mn, and B is Al, Fe3+ or Cr.

Garnet as Gemstone

• Types of garnet include pyrope, almandine, spessartine, grossular, andradite, uvarovite and hydrogrossular. All but uvarovite have uses as gemstones. The most valuable is a green andradite called demantoid, which comes from the Ural Mountains.