Prasiolite

Also known as Green Amethyst this yellow-green to green variety of  quartz that is cut into faceted stones for use in jewelry or collectors. It is produced by the three processes described:Heat-Treated> Most prasiolite is produced by heating natural amethyst in a laboratory oven to about 500 degrees Celsius. This heating changes the amethyst's color from purple to green or yellowish green. Irradiated > A small amount of prasiolite is produced by irradiating natural amethyst. This produces prasiolite with a light green color. The green color is often unstable and can fade to colorless if the stone is exposed to temperatures over about 150 degrees Celsius. Natural > Another small amount of amethyst is heated in a natural processes. It is found where an amethyst-bearing rock unit has been heated by younger lava flows or nearby intrusions. -WET pic. (4 oz.)