Prasiolite is a yellow-green to green variety of quartz. It can be produced by:
Amethyst that is naturally heated by lava flows;
Irradiating Amethyst to about 302º Fahrenheit, turning the purple Amethyst to a pale green. However, this method tends to fade to colorless over time.
Heating Amethyst to about 935º Fahrenheit, turning purple Amethyst to a green or yellowish green color. This method is how most Prasiolite on the market is produced.
Prasiolite is misnamed as Green Amethyst.