Amethyst has been a prized gem for centuries. Amethysts are the most valuable variety of quartz, and were one of the first gemstones used by people around the world. The Greeks believed that drinking wine from an amethyst cup would prevent intoxication. Royalty has also favored the purple gemstone, and at one time amethysts were reserved for royalty alone.
The rich purple color is due to iron and manganese inclusions. Exposure to heat or irradiation can produce a yellow to orange color (citrine) or a pale green color (prasiolite). The hexagonal crystal structure can vary in size from microcrystalline drusy to large scepters and often forms inside agate geodes.