Amethyst is a variety of Quartz that gets its color from the traces of iron it contains. Its name comes from the Greek "Amethustos", which means "Who preserves from drunkenness".
The legend
In Greek mythology, the story is about Dionysus, the god of the vine, wine, celebration and its excesses. Dionysus is the son of Zeus. He claimed a nymph from the procession of Artemis named Amethystos, unfortunately for him, the latter wished to remain chaste. She asked Artemis to preserve her. Artemis then transformed her into a sparkling white stone (Quartz) to save her from the incessant demands of Dionysus.
The latter, mad with grief on realizing what had happened, cried over the stone. Her tears flowed into her wine glass which eventually spilled and spilled onto the rock, tinging the purple Quartz now known as Amethyst.
The belief
From its name, it was thought that wearing an Amethyst protected against poisoning. The Greeks and Romans carried it with them and made Amethyst containers to prevent drunkenness and intoxication.
More informations
If you want to know more, consult the page dedicated to Amethyst.