Ametrine, also known as “trystine”, is a naturally occurring variety of quartz. It is a blend of amethyst and citrine with parts of purple and yellow or orange. almost all of it is mined in Bolivia.
The different colors in the Ametrine are caused by varying levels of the iron inside and it’s degree of oxidation. The yellow citrine part has oxidized iron while the purple amethyst part remains unoxidized. The difference in oxidation happens when the crystal is forming and is dependent on how the heat is distributed over the crystal.