mineral

Smoky Quartz

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Brownish-grey, smoky yellow-brown to nearly black; Luster: Vitreous (glassy); Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Brownish-grey, smoky yellow-brown to nearly black
Luster: Vitreous (glassy)

Identified March 29, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous and metamorphic rocks, particularly pegmatites and hydrothermal veins. The smoky color is caused by natural gamma radiation from the surrounding rock that activates aluminum impurities within the crystal structure.

Uses & applications

Used primarily in jewelry (faceted gemstones, beads), ornamental carvings, and by crystal collectors. Historically used in early 12th-century China to make the first 'sunglasses' from flat panes of the mineral.

Geological facts

The dark color can be removed by heating the stone to 300-400 degrees Celsius. It is the national gem of Scotland, where it is often referred to as 'Cairngorm' after the mountain range where it is found.

Field identification & locations

Identify in the field by its smoky transparency, six-sided prism habit (if crystal faces are present), and lack of cleavage. Common locations include Brazil, Switzerland (the Alps), USA (Colorado and New Hampshire), and Madagascar.