According to legend, an ordinary mortal insulted Bacchus, so he created a team of tigers to destroy the next hapless mortal who crossed his path. Saly, the mortal turned out to be a beautiful maiden named Amethyst. Diana, the goddess of the moon, was watching, and she did what she could to protect Amethyst-- she turned her into a statue of pure crystal quartz, impervious to the tiger's claws. But when Bacchus saw how beautiful Amethyst had been, he regretted his foolish, poorly planned display of bad temper. He wept bitter tears of dark wine over the crystal and stained it purple.
[Taken from Crystals for Beginners: a guide to collecting & using stones & Crystals by Corrine Kenner]