mineral

Smoky Quartz

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Brownish-grey to yellowish-brown; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Brownish-grey to yellowish-brown
Luster: Vitreous (glassy)

Identified March 15, 2026More mineral →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brownish-grey to yellowish-brown; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed in igneous or metamorphic environments when silicon dioxide is subjected to natural radiation from surrounding granite or pegmatite rocks, causing structural defects that trap electrons and create the characteristic smoky color. Ages can range from millions to over a billion years.

Uses & applications

Commonly used in lapidary for jewelry, beads, and carvings. Historically used for ancient Chinese sunglasses and in industrial manufacturing of oscillators for electronics (though synthetic quartz is more common now). Popular among mineral collectors.

Geological facts

The brown color is not due to impurities but rather the effect of gamma irradiation on aluminum traces within the crystal lattice. Massive geodes of smoky quartz found in the Swiss Alps have been known for centuries as 'Grenzsteine'.

Field identification & locations

Identify in the field by its hexagonal crystal habit (if not tumbled), greasy-to-glassy luster, and the fact that it can scratch glass but cannot be scratched by a steel knife. Common in Brazil, Colorado, and the Swiss Alps. Often found in pockets within granite.