mineral
Smoky Quartz
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Brownish gray to black; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: Indistinct/Conchoidal fracture; Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Brownish gray to black
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 7 (Mohs scale); Color: Brownish gray to black; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: Indistinct/Conchoidal fracture; Specific Gravity: 2.65
Formation & geological history
Formed in igneous or metamorphic rocks, particularly pegmatites and hydrothermal veins. The color is caused by natural irradiation of aluminum-bearing quartz over millions of years.
Uses & applications
Used in gemstone jewelry, decorative carvings, watchmaking (piezoelectric properties), and as a popular collector specimen.
Geological facts
The dark color is often the result of free silicon formed from silicon dioxide by natural radiation. It is the national gem of Scotland, where it is known as Cairngorm.
Field identification & locations
Identify by its smoky translucence, lack of cleavage, and inability to be scratched by a steel blade. Commonly found in Brazil, Madagascar, and the Swiss Alps.
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