Ametrine
Ametrine, also known as trystine, golden amethyst, or by the trade name bolivianite, is a variety of quartz with alternating zones of purple and yellow-orange coloration. Its name is a portmanteau of amethyst and citrine. While ametrine is commonly referred to as a combination of these two quartz varieties, some sources claim this is not accurate. Almost all commercially available ametrine is mined in Bolivia.
Color
Ametrine, as its name suggests, is commonly believed to be a combination of citrine and amethyst in the same crystal. However, sources do not agree that the yellow-orange quartz component of ametrine may properly be called citrine. Like the purple color of amethyst, the yellow color in ametrine originates from trace amounts of iron in the crystal structure. The difference in coloration is due to the iron existing in different oxidation states. The yellow segments have been oxidized by heat, while the amethyst segments remain unoxidized. Some sources define citrine solely as quartz with its color originating from aluminum-based color centers, similar to those of smoky quartz. This definition excludes any amethyst that has been oxidized by heat. Accordingly, the yellow quartz in ametrine would not be considered true citrine.Origin
Naturally occurring ametrine is sourced almost exclusively from a single mine in Bolivia. Deposits also exist in Brazil and India. The different oxidation states occur due to there being a temperature gradient across the crystal during its formation. However, most ametrine on the market is created by partially heating or irradiating amethyst.Ametrine in the low price segment may stem from synthetic material. Green-yellow or golden-blue ametrine does not exist naturally. Synthetic ametrine is grown with the hydrothermal method using solutions doped with specific elements, followed by irradiation of the created crystals.