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smoky quartz

Smoky quartz is a variety of color of crystalline quartz. It goes from a light yellowish brown to a brown so dark that it seems to be black. The least wanted specimens have a greyish brown color. When cut like a gemstone, orange brown to reddish brown stones are preferred by meny people.

It is often found in the form of large crystals of excellent transparency with few inclusions.

The color of smoky quartz is produced when natural radiation, emitted by the surrounding rock, activates the color centers around the aluminum impurities inside the crystalline quartz. Amethyst is formed in the same way, from the activation of the color centers around the iron impurities.

Learn more about smoky quartz: Wikipedia