mineral

Smoky Quartz

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Brownish-grey to black; Luster: Vitreous; Crystal structure: Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Brownish-grey to black
Luster: Vitreous

Identified February 20, 2026More mineral →

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Physical properties

Hardness: 7 (Mohs scale); Color: Brownish-grey to black; Luster: Vitreous; Crystal structure: Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Forms in igneous and metamorphic rocks, particularly pegmatites and hydrothermal veins. Its dark color results from natural irradiation of aluminum-containing quartz during its primary formation over millions of years.

Uses & applications

Used extensively in jewelry as gemstones, in lapidary work for carvings, and as decorative display specimens. Historically used for one of the first known pairs of sunglasses in 12th century China.

Geological facts

The dark color is caused by free silicon formed from silicon dioxide by natural irradiation. When it is nearly opaque, it is known as 'Morion'. It is the national gem of Scotland, where it is often called 'Cairngorm'.

Field identification & locations

Identified by its hexagonal crystal habit (if uncut), vitreous luster, and varying degrees of brown-to-grey transparency. Commonly found in Brazil, Madagascar, Switzerland, and the United States (Colorado). To identify in the field, check for hardness (cannot be scratched by steel) and lack of cleavage.