mineral

Smoky Quartz

Silicon dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Grayish-brown to black; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: Indistinct; Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Grayish-brown to black
Luster: Vitreous (glassy)

Identified July 21, 2026More mineral →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grayish-brown to black; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: Indistinct; Specific Gravity: 2.65.

Formation & geological history

Formed in igneous and metamorphic rocks, particularly granite pegmatites. The dark color is caused by natural radiation from surrounding rocks acting on trace amounts of aluminum within the quartz structure.

Uses & applications

Used in jewelry, decorative ornaments, and by collectors. In industry, it was historically used for early sunglasses in China and is currently used in piezoelectric devices if high purity.

Geological facts

The dark color can be deepened through artificial irradiation or turned yellow (into citrine) through heat treatment. Cairngorm is a famous variety found in the Cairngorm Mountains of Scotland.

Field identification & locations

Identify by its smoky translucence, lack of cleavage, and ability to scratch glass. It is common in alpine veins and pegmatite deposits worldwide, including Brazil, Madagascar, and the USA (Colorado).