Smokey Quartz (Tumbled Crystal)
What is Smoky Quartz?
Smoky quartz is a color-variety of crystalline quartz. It ranges from a light yellowish brown to a brown that is so dark that it appears to be black. Less-desirable specimens have a grayish brown color. When cut as a gem, stones with an orangish brown to a reddish brown color are preferred by many people.
Smoky quartz is an inexpensive gem materialbecause it is abundant, found in many locations, and its brown color is not currently in high demand. It is often found in large crystals of excellent transparency with few inclusions.
The color of smoky quartz is produced when natural radiation, emitted from the surrounding rock, activates color centers around aluminum impurities within the crystalline quartz. Amethyst forms in a similar way, from the activation of color centers around iron impurities.