mineral

Smoky Quartz

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Gray to brownish-black translucent tint; Luster: Vitreous (glassy); Crystal structure: Hexagonal/Trigonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray to brownish-black translucent tint
Luster: Vitreous (glassy)

Identified April 13, 2026More mineral →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray to brownish-black translucent tint; Luster: Vitreous (glassy); Crystal structure: Hexagonal/Trigonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.65

Formation & geological history

Formed in igneous and metamorphic rocks (especially granitic pegmatites) through the natural irradiation of aluminum-bearing clear quartz over millions of years.

Uses & applications

Used in jewelry as gemstones, ornamental carvings, and historical use in early optical lenses/sunglasses (pioneered in 12th century China).

Geological facts

The dark color is caused by free silicon formed from silicon dioxide by natural irradiation. It is the national gemstone of Scotland, where it is known as 'Cairngorm'.

Field identification & locations

Identify in the field by its hardness (will scratch glass), lack of cleavage, and translucent 'smoky' gray appearance. Commonly found in mountainous granite regions like the Alps, Brazil, or Colorado.