Ametrine, also known as “Trystine” or its trade name “Bolivianite” is a very unique kind of gemstone. It is a rare combination of purple Amethyst and golden Citrine in one stone. Both Amethyst and Citrine are part of the Quartz family of minerals but their distinct rich colors come from different reactions during their growth process.
Quartz is made up of the elements Silicon and Oxygen, but to create the bold colors of the Citrine and Amethyst variations Iron must be present in the compound. Amethyst generally has a smaller amount of Iron than Citrine. For Amethyst to become purple there must be a certain amount of gamma radiation during the growth process to oxidize the Iron from a 3+ to a 4+ state.
This is such a rare occurrence in nature that virtually all of the world’s true natural Ametrine comes from only one mine near Santa Cruz, Bolivia in the Andes mountain range. There are trace amounts of Ametrine found in India and Brazil but they are very light in color and there are very few gem quality specimens. Most of the Ametrine found in India or Brazil are irradiated in a lab to increase color saturation.
Today Ametrine has become quite popular and many “look-a-likes” and false Ametrine have entered the market being sold as Ametrine. It is possible to create Ametrine synthetically, but requires a very specific process to get the color sections to come out just right. There are other false “Ametrine” being sold which have very different color combinations that are far from true Ametrine and could not possibly be natural. True Ametrine is always a combination of purple Amethyst and golden Citrine.
Here are a couple of really cool articles that go further in depth about Ametrine if you are interested in finding out more specifics:
Ametrine Information: http://minerals.gps.caltech.edu/Ametrine/Index.html
Tour of Bolivian mine: http://www.gia.edu/gia-news-research-In-Search-of-Ametrine