mineral

Smoky Quartz

Silicon Dioxide (SiO2)

Hardness 7 on Mohs scale; translucent to transparent grayish-brown to smoky gray color; vitreous (glassy) luster; trigonal crystal system; no true cleavage, displays conchoidal fracture; specific gravity 2.65.

Identified July 25, 2026More mineral →

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Physical properties

Formation & geological history

Forms in igneous rocks like granite and pegmatites, as well as high-temperature hydrothermal veins. The smoky gray color is caused by natural irradiation acting on aluminum impurities within the crystal lattice.

Uses & applications

Used widely as an gemstone for jewelry, lapidary carvings, ornamental decorations, and as popular specimens in mineral collections.

Geological facts

Smoky quartz is the national gem of Scotland, where it is known as 'Cairngorm' after the Cairngorm Mountains where fine specimens were historically found. Ancient Chinese judges used flat panes of smoky quartz as early sunglasses in the 12th century.

Field identification & locations

Identified in the field by its hardness (scratches glass), glass-like conchoidal fracture, lack of cleavage, and translucent grayish-smoky color. Found globally, with notable deposits in Brazil, Madagascar, Scotland, Switzerland, and the United States (Colorado).