Amethyst can occur as crystals that are six sided on either end. It also forms as drusy which are crystalline crusts covering the host rock. It is found inside geodes and in alluvial deposits all around the world and occurs in both crystalline or massive forms. When manganese is present in clear quartz amethyst is produced, while the amount of iron contained in the specimen accounts for the depth of purple
The colour forming agent in Amethyst is iron, which gives it some affinity with the planet Mars. When heat-treated amethysts can change colour from clear to green and reddy-brown. This process is done to create commercial specimens such as green amethyst and commercial citrine which are often just purple amethysts of lower quality heated to a specific point.
Artigas, Uruguay and neighboring Brazilian state Rio Grande do Sul are large world producers exceeding in quantity Minas Gerais, as well as Mato Grosso, Espirito Santo, Bahia, and Ceará states, all amethyst producers of importance in Brazil. It is also found and mined in South Korea.
Amethyst is the official state gemstone of South Carolina. Several South Carolina amethysts are on display at the Smithsonian Museum of Natural History.