Ametrine, also known as Trystine or Bolivianite, is a variety of Quartz (SiO2) with a Mohs hardness of 7. Ametrine crystals are made of alternating sectors of purple Amethyst (caused by the presence of iron with an oxidation number of 4, Fe(+4), built into its crystal framework as a replacement for Si and subsequent irradiation from radioactive elements) and yellow to orange Citrine (caused either by inclusions of iron compounds or by iron ions, Fe3+, built into the crystal lattice).
Although the most well known source for Ametrine is the Anahi Mine (a 6250 acre site near the town of Puerto Suárez in the eastern tropics of Bolivia, very near the border of Brazil), commercial-grade deposits have also been found in India and Brazil.