mineral
Smoky Quartz
Silicon Dioxide (SiO2) with aluminum impurities
Hardness: 7.0 Mohs. Color: Translucent to opaque brown-gray to black. Luster: Vitreous (glassy). Crystal Structure: Trigonal. Cleavage: Indistinct. Specific Gravity: 2.65.
- Hardness
- 7
- Color
- Translucent to opaque brown-gray to black
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 7.0 Mohs. Color: Translucent to opaque brown-gray to black. Luster: Vitreous (glassy). Crystal Structure: Trigonal. Cleavage: Indistinct. Specific Gravity: 2.65.
Formation & geological history
Formed in igneous rocks like granite and pegmatites through the natural irradiation of aluminum-bearing quartz over millions of years. It occurs in hydrothermal veins and metamorphic rocks as well.
Uses & applications
Used widely in lapidary for jewelry, ornamental carvings, and decorative crystals. Historically used for making the first sunglasses in 12th century China.
Geological facts
The dark color is caused by free silicon formed from silicon dioxide by natural irradiation of the crystal at the time of its growth or later. Cairngorm is a popular name for smoky quartz found in the Cairngorm Mountains of Scotland.
Field identification & locations
Identify by its smoky-brown color, transparency, and hardness (it will scratch glass but not a steel file). It is commonly found in Brazil, Madagascar, the Swiss Alps, and the Pikes Peak area of Colorado.
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