mineral

Smoky Quartz

Silicon Dioxide (SiO₂)

Hardness: 7 (Mohs scale); Color: Brown, grey, to black; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: Indistinct (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Brown, grey, to black
Luster: Vitreous (glassy)

Identified April 25, 2026More mineral →

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Physical properties

Hardness: 7 (Mohs scale); Color: Brown, grey, to black; Luster: Vitreous (glassy); Crystal Structure: Hexagonal (trigonal); Cleavage: Indistinct (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed in igneous and metamorphic rocks, particularly granite and pegmatite. The smoky color is caused by natural irradiation of aluminum-bearing quartz over millions of years within the Earth's crust.

Uses & applications

Used primarily in jewelry, ornamental carvings, and by crystal collectors. Historically used in China for early sunglasses and in electronics as a piezoelectric material.

Geological facts

Smoky quartz is the national gem of Scotland, where it is known as 'Cairngorm' because it is found in the Cairngorm Mountains. Extremely dark, opaque specimens are often called 'Morion'.

Field identification & locations

Identify in the field by its glassy luster, lack of cleavage, and its ability to scratch glass. It is commonly found in mountain ranges worldwide, particularly in Brazil, the Swiss Alps, and the United States (Colorado and Maine).