Rough Ametrine. credit: GoldenHourMinerals

A bicolor variety of quartz that is purple amethyst on one side and orange citrine on the other, ametrine occurs naturally only at the Anahí Mine in the Sandoval Province of eastern Bolivia.

Ametrine is composed of silicon dioxide (SiO2 ) and it is a tectosilicate, which means it has a silicate framework linked together through shared oxygen atoms.

Ametrine is a mix of both Ametrine and Citrine producing a mixture of purple and yellow/orange crystal colours. It is produced under such exceptional and improbable conditions, requiring a perfect combination of iron presence and differing temperatures within a very confined area, that it has occurred only once that we know of, in only one known place in the world: Santa Cruz, Bolivia.

The Anahí mine is the one and only bolivianite mine known to exist anywhere on Earth. The mineralization is found in the northern part of a hill formed by limestones and dolomites, and has been generated by silicification of the limestones belonging to the Murcielago Group, deposited in the Precambrian, between 500 and 900 million years ago. Ametrine crystals are found in hydrothermal breccias.

The Anahi ametrine crystals range in size from 10 to 30 cm in length and 4 to 12 cm in diameter. When sliced and polished, the interior of the crystals show the typical color zoning. The amethyst and citrine zones run from top to bottom, parallel to the crystal’s c-axis.

Ametrine in the low price segment may stem from synthetic material. Green-yellow or golden-blue ametrine does not exist naturally. This gem only exists in Bolivia, it comes from the Ricón del Tigre area, from the Anahí mine.