Every amethyst starts as ordinary quartz, the most common mineral on the earth's surface. What turns it into February's purple birthstone is a mix of trace iron, natural radiation and a great deal of time, usually inside a hollow pocket of volcanic rock.

Quartz With a Touch of Iron

Chemically, amethyst is silicon dioxide, the same as clear rock crystal. As the crystal grows, tiny amounts of iron find their way into its structure. On their own they do not make it purple. Over long periods, low-level natural radiation from surrounding rocks changes those iron atoms, creating what gemologists call color centers, and those absorb light in a way our eyes see as purple.

That is why color can vary inside a single crystal: the tips of amethyst crystals are often darker than their bases, where less iron was taken in.

Born in Volcanic Geodes

Many of the world's finest amethysts formed in basalt, a volcanic rock. When lava cooled, gas bubbles left hollow pockets. Over millions of years, mineral-rich water seeped through the rock and slowly deposited quartz on the walls of those cavities, building inward-pointing crystals. Crack one open and you have a geode: a plain stone shell hiding a lining of purple points.

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Where the Finest Amethyst Comes From

Heat, Citrine and Ametrine

Amethyst's color is sensitive to heat. Warmed to several hundred degrees Celsius, the purple fades and the stone turns yellow or orange, and much of the citrine sold today began as amethyst treated this way. In rare deposits, nature does something similar inside a single crystal, producing ametrine, a quartz that is half purple and half gold.

The same sensitivity is why amethyst should be kept away from strong heat and long, direct sunlight, which can slowly lighten its color.

Hardness and Wear

Like all quartz, amethyst rates 7 on the Mohs scale. That is hard enough to resist everyday dust and scratches, so it wears well in earrings, pendants and rings with a protective setting. Harder stones such as diamond can scratch it, so it is best stored on its own.

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A Stone With a Long Story

The name comes from the ancient Greek amethystos, meaning "not intoxicated", from an old belief that the stone kept its wearer clear-headed. Purple was long a color of royalty, and amethyst appears in crowns and church jewelry across Europe. Today it is the birthstone for February and the traditional gem for a 6th anniversary.

Ready to choose a piece? Read our amethyst jewelry guide or explore amethyst jewelry.

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