Ametrine is a macrocrystalline variety of Quartz that occurs rarely in nature. Most Ametrine in the market today is simulated Amethyst. When Amethyst is heated, it turns varied shades of yellow. For Ametrine to occur naturally, iron impurities, combined with differing oxidation states are subjected to varied temperature. The temperature would need to be slightly higher on some of the surfaces and slightly cooler on others. An example of this would be where one side of the crystal was facing a heat source and the delicate balance of the two temperatures was maintained during the crystallization of the quartz. This is how natural Ametrine is formed in nature. Amethyst subjected to the same type of conditions will also produce Ametrine (stimulated or heated process).
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