As far as amethyst goes...what a beautiful story:
According to Greek mythology, Bacchus was insulted by a human and swore revenge (via a tiger mauling) on the next human he saw. Diana saw this poor human woman named Amethyst heading towards Bacchus so Diana took pity on her and turned her into a quartz statue to protect her from the tiger. Bacchus was so regretful of his actions that he cried tears of wine on to the beautiful Amethyst, hence the gems beautiful color!