Garnets are commonly found in a variety of jewelry, and the stone is recognized as the birthstone for the month of January. Most commonly found in the United States, India and Australia, garnets form in the shape of crystals when found in the earth. Once mined, their quality can be ascertained. Clearer, higher-quality gems will be used for jewelry. Lesser quality stones might be sold for abrasive materials. Garnets might contain traces of other minerals and elements, such as aluminum.
The formation of garnets always takes place in metamorphic rock. A metamorphic rock is either a sedimentary or igneous rock which has been changed, or metamorphosized, by some force. The most common forces are heat, pressure or some combination of both. As the rocks change, conditions might form garnets inside the metamorphic stones. As a result, garnet is commonly found in stones like gneiss and schist. There is however a second way that garnets could be formed, though it is not as common as formation by usual, metamorphic processes.
While all garnets are formed in metamorphic rock, not all of them are formed by the processes that made the metamorphic rocks. Once two metamorphic rocks have been formed, they lay in the earth next to each other like separate layers on a cake. As the earth shifts and moves, these metamorphic rocks might grind against each other. As this grinding happens, garnets could be formed. Garnets formed from the grinding of metamorphic rocks often contain smaller chunks of metamorphic rock inside them, marking them out as different from garnets that were formed along with the metamorphic rock that they are found inside.