mineral

Smoky Quartz

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Brownish grey, black, translucent to opaque; Luster: Vitreous; Crystal structure: Hexagonal (trigonal); Cleavage: Indistinct; Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Brownish grey, black, translucent to opaque
Luster: Vitreous

Identified May 17, 2026More mineral →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brownish grey, black, translucent to opaque; Luster: Vitreous; Crystal structure: Hexagonal (trigonal); Cleavage: Indistinct; Specific gravity: 2.65

Formation & geological history

Formed in igneous and metamorphic rocks like granite and gneiss. The dark color is caused by natural gamma radiation from the surrounding rock that activates aluminum impurities within the quartz structure.

Uses & applications

Used primarily in jewelry as a gemstone, decorative ornaments, and by mineral collectors. In industry, high-quality quartz was historically used for oscillators and piezoelectric devices.

Geological facts

Smoky quartz is the national gem of Scotland, where it is known as Cairngorm after the mountain range where it is found. It can range from light tan to a nearly opaque 'Morion' variety.

Field identification & locations

Identify in the field by its crystal habit (six-sided prisms with pyramids) and the fact that it can scratch glass but cannot be scratched by a steel knife. Commonly found in pegmatites and Alpine-type veins.