mineral
Smoky Quartz with possible inclusion
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brownish-black, to translucent; Luster: Vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, brownish-black, to translucent
- Luster
- Vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brownish-black, to translucent; Luster: Vitreous; Crystal Structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Forms in igneous and metamorphic rocks, particularly pegmatites and hydrothermal veins, where natural radiation from surrounding rocks colorizes the clear quartz over millions of years.
Uses & applications
Used extensively in jewelry, as gemstone specimens for collectors, and in the manufacturing of optical instruments and electronics.
Geological facts
The smoky color is caused by free silicon formed from silicon dioxide by natural irradiation. It is the national gem of Scotland, where it is known as Cairngorm.
Field identification & locations
Identify by its hardness (scratches glass), lack of cleavage, and translucent smoky gray/brown color. Found globally, with notable deposits in Brazil, Madagascar, and the Swiss Alps.
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