Quartz is often found lining the insides of geodes. So it's no wonder that geodes sometimes contain amethysts too. An amethyst's color can range from a faint mauve to a rich purple. It's not clear why they're purple. Some scientists believe the purple color arises from the amethysts' iron oxide content, while others attribute the color to manganese or hydrocarbons.
Amethysts are very sensitive to heat.
When heated to 400 or 500 degrees Celsius, an amethyst's color changes to a brownish-yellow or red. Under some circumstances, the stones can turn green when heated. Heat may even transform an amethyst into a naturally-rare mineral called citrine. And even without heating, the violet color of an amethyst may fade over time. The amethyst has a rich history of lore and legend.