Amethyst

Amethyst is the purple variety of quartz, SiO₂. Its color comes from traces of iron, activated by natural radiation. Heat removes it: heated amethyst turns yellow to orange and is the source of most citrine on the market. Some amethyst also fades in strong sunlight. The largest quantities come from geodes in the basalts of Rio Grande do Sul in Brazil and Artigas in Uruguay. Collectors also know the long, pale prisms of Veracruz and the deep purple crystals of Guerrero in Mexico, the amethyst of the Urals, Thunder Bay in Ontario, and scepters and phantoms from the Brandberg and the Goboboseb Mountains in Namibia. The name comes from the Greek amethystos, not drunk; the stone was thought to protect against drunkenness.