Ametrine semi precious stone naturally occurring variety of quartz. Colour zoned quarz being made up normally half and half of amethyst and citrine ( citrine is naturally heated amethyst which then changes from purple to yellow). It is a mixture of amethyst and ( citrine . The best know depsoits today are Brazil and Boliva. The color of the zones visible within ametrine is due to differing oxidation states of iron within the crystal. The different oxidation states occur due to there being a temperature gradient across the crystal during its formation. Also known as trystine or by its trade name as bolivianite. Ametrine is a birthstone for the zodiac sign of Libra. The only significant source of natural ametrine is the Anahí mine, in eastern Bolivia.