mineral

Smoky Quartz

Smoky Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Brown, grey, or black; Luster: Vitreous (glass-like); Crystal structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Brown, grey, or black
Luster: Vitreous (glass-like)

Identified February 15, 2026More mineral →

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Physical properties

Hardness: 7 (Mohs scale); Color: Brown, grey, or black; Luster: Vitreous (glass-like); Crystal structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Forms in igneous and metamorphic rocks, particularly granites and pegmatites. The smoky color is caused by natural radiation from surrounding rocks acting on trace amounts of aluminum within the silicon dioxide crystal lattice.

Uses & applications

Used primarily in jewelry, crystal healing practices, and as collector specimens. Occasionally used in optical instruments and electronics as a source of high-purity silica.

Geological facts

The dark color is unstable at high temperatures; if heated to 300-400°C, the smoky color can be lost or turn yellow (citrine). It is the national gemstone of Scotland, where it is known as 'Cairngorm'.

Field identification & locations

Identify in the field by its characteristic brown translucency, lack of cleavage, and ability to scratch glass. Commonly found in Brazil, Madagascar, and the Swiss Alps.