mineral

Smoky Quartz

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Grey, brown, to near black translucency; Luster: Vitreous (glassy); Crystal structure: Hexagonal (trigonal); Cleavage: Indistinct; Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Grey, brown, to near black translucency
Luster: Vitreous (glassy)

Identified July 12, 2026More mineral →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grey, brown, to near black translucency; Luster: Vitreous (glassy); Crystal structure: Hexagonal (trigonal); Cleavage: Indistinct; Specific Gravity: 2.65.

Formation & geological history

Forms in igneous and metamorphic rocks, particularly pegmatites and hydrothermal veins. The smoky color is caused by natural irradiation of aluminum-bearing quartz over long geological periods.

Uses & applications

Used widely in jewelry (rings, pendants), ornamental carvings, and by crystal collectors. Historically used in early Chinese sunglasses and for decorative seals.

Geological facts

Smoky quartz is the national gem of Scotland, where it is known as 'Cairngorm' after the Cairngorm Mountains. The dark color can sometimes be lightened by heat treatment.

Field identification & locations

Identify in the field by its crystal habit (six-sided prisms with pyramids), lack of cleavage, and characteristic translucent 'smoke' color. Commonly found in Brazil, USA (Colorado), and the Swiss Alps.