Amethyst is formed when water on the surface of the Earth interacts with silicon dioxide, or SiO2 and causes it to dissolve. After conditions change to cause the solution to evaporate or cool, the silicon dioxide will precipitate to form quartz crystals. Amethyst is a type of quartz that comes in varying shades of purple.
The name "amethyst" comes from the Ancient Greek and means "not intoxicated." It was named based on the belief that the gem could keep people from becoming drunk. Amethyst is the birthstone for February and the official gemstone of South Carolina. It is considered a semiprecious stone and is often used in jewelry.
Amethyst crystals tend to form six-sided prisms with a six-sided pyramid on the end. It gets its purple color from iron impurities, trace elements and irradiation. As of 2015, most of amethyst used in jewelry comes from Brazil, although historically it was mined primarily in the Ural Mountains in Russia. In North America, amethyst is primarily mined in Thunder Bay, Ontario. Synthetic amethyst is created by irradiating clear quartz.
Other gems that are formed from the interaction of surface water and minerals include agate and opal, which are silicon dioxide based, and turquoise, which is formed from minerals containing copper.