Amethyst

It is a semiprecious stone and is the traditional birthstone for February. http://dictionary.reference.com/browse/amethyst

1250-1300;  Latin amethystus, Greek améthystos not intoxicating, not intoxicated (so called from a belief that it prevented drunkenness)

The ancient Greeks wore amethyst and made drinking vessels decorated with it in the belief that it would prevent intoxication. It is one of several forms of quartz.