Amethyst

Amethyst is the best known and most valuable form of quartz.  Its name is derived from the Greek amethustos (not drunken); ancient belief held that anyone wearing an amethyst could not become intoxicated.  Amethyst is found in numerous areas of the world, including Canada, Brazil, and United States.
Some believe it protects from any over-indulgence.  It is suppose to help you get in touch with your intuition.  It also bestows stability, strength, invigoration and peace.