Ametrine

The only commercial source of natural ametrine is the Anahí mine in eastern Bolivia (Puerto Suárez Municipality, Germán Busch Province, Santa Cruz), close to the Brazilian border. The remote mine also produces natural amethyst and citrine; ametrine from it began appearing on the market in the 1970s.

Ametrine crystals consist of alternating purple and yellow-to-orange color sectors; slabs cut perpendicular to the c-axis look somewhat like a pinwheel. The purple sectors lie under the positive rhombohedral faces and the yellow sectors under the negative ones. According to Mindat, the yellow-orange sectors are colored by inclusions of iron compounds (ferruginous quartz) rather than being true citrine, so on heating the purple sectors pale while the yellow-orange sectors keep their color. Its gemological constants are those of quartz. Fine stones show a roughly half-and-half color distribution with a sharp boundary, and most faceted ametrine is eye-clean.

Ametrine is rarely treated but may have filled fractures. Synthetic ametrine has been grown hydrothermally in Russian laboratories, and distinguishing natural from synthetic material relies on microscopic examination.

Like amethyst and citrine, ametrine rates 7 on the Mohs scale and has good toughness, so it suits all jewelry types, including rings, with care to avoid scratching. Abrupt temperature changes can fracture it, some colors can fade with prolonged exposure to intense light, and it can be damaged by hydrofluoric acid, ammonium fluoride and alkaline solutions. Warm, soapy water is always safe; ultrasonic cleaning is usually safe except for rare dyed or fracture-filled stones; steam cleaning is not recommended, and it should not be exposed to heat.

According to legend, a Spanish conquistador received the mine as a dowry when he married a native princess named Anahí, and introduced the gem to Europe in the 1600s by presenting specimens to his queen. The mine's location was then lost for more than three centuries. It was rediscovered in the 1960s, ametrine reappeared on the market in the 1970s, and the mine is named Anahí after the legendary princess.