Ametrine
| Property | Details |
|---|
| Mineral | Quartz (amethyst-citrine bicolor) |
| Mohs Hardness | 7 |
| Refractive Index | 1.544 – 1.553 |
| Birthstone | Not a traditional birthstone |
| Major Sources | Anahí mine, Bolivia (primary source worldwide) |
| Treatments | Usually untreated; heat can shift color balance |
Overview
Ametrine is a rare and fascinating bicolor gemstone that combines amethyst purple and citrine gold in a single crystal. This natural phenomenon occurs when different temperature and oxidation conditions exist across zones within the same quartz crystal during formation, causing iron impurities to produce both colors simultaneously. The result is a gemstone unlike any other—two distinct colors meeting in one stone with a sharp, dramatic boundary.
How It Forms
Ametrine forms when a quartz crystal grows under conditions where temperature varies across its structure. In zones where the temperature is lower, iron impurities adopt an oxidation state that produces amethyst’s purple color. In warmer zones, a different oxidation state produces citrine’s golden hue. This happens naturally in a single crystal, creating the characteristic bicolor zoning. The Anahí mine in eastern Bolivia, discovered in the 17th century by Spanish conquistadors, is essentially the world’s only commercial source of natural ametrine.
Colors & Patterns
Classic bicolor: A clean split between rich purple and warm gold—the most desirable pattern. Skilled cutters orient the rough to maximize the contrast between zones. Blended: Some stones show a softer transition between colors. Fantasy cuts: Master gem cutters sometimes create concave or artistic cuts in ametrine that produce kaleidoscopic color patterns, reflecting both colors in complex internal reflections. The most valued ametrine displays vivid, saturated purple and gold in roughly equal proportions with a clean, distinct color boundary.
Quality & Value Factors
The finest ametrine combines deep, saturated amethyst purple with rich citrine gold in a roughly 50/50 split with a sharp, clean boundary. Clarity should be eye-clean or better—most gem-quality ametrine is naturally inclusion-free. Size is important: the bicolor effect becomes more dramatic and visually striking in larger stones, so gems above 5 carats are particularly desirable. Because nearly all natural ametrine comes from a single mine, supply is inherently limited, though prices remain accessible compared to many other colored gemstones.
Care & Cleaning
Ametrine shares the durability of other quartz gemstones at 7 on the Mohs scale. Clean with warm soapy water and a soft brush. Ultrasonic cleaners are generally safe. Like amethyst, ametrine can fade with prolonged exposure to intense direct sunlight or high heat, so store away from windows and avoid leaving it on a car dashboard or similar locations. With basic care, ametrine is a durable and striking choice for rings, pendants, and earrings.