Ametrine, also known as Trystine or by its trade name as Bolivianite, is a naturally occurring variety of quartz. It is a mixture of Amethyst and Citrine with zones of purple and yellow or orange. Almost all commercially available Ametrine is mined in Bolivia. Brazil and India also have Ametrine deposits.
The different states of oxidation of iron within the crystal make the different colors appear in different zones. A temperature gradient along the crystal during its formation can cause the different states of oxidation. Artificial Ametrine can be created by differential heat treatment given to Amethyst.
Most Ametrine in the low price segment stem from synthetic material. Since 1994 a Russian laboratory has perfected the industrial production of bi-colored quartz crystals which are later irradiated to bring out the typical Ametrine colors. Green-yellow or golden-blue Ametrine does not exist in nature.