mineral

Smoky Quartz

SiO2 (Silicon Dioxide)

Hardness: 7 on Mohs scale. Color: Grayish-brown to black, translucent to nearly opaque. Luster: Vitreous (glassy). Crystal Structure: Hexagonal (trigonal). Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

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

Identified March 7, 2026More mineral →

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Physical properties

Formation & geological history

Formed in igneous or metamorphic rocks (especially pegmatites). The smoky color is caused by natural radiation from surrounding rocks activating aluminum impurities within the crystal lattice. Usually occurs in crustal rocks of various geological ages.

Uses & applications

Used primarily in lapidary work for jewelry (cabochons and gemstones), ornamental carvings, and as a popular specimen for mineral collectors. Some industrial use in electronics, though synthetic quartz is now more common.

Geological facts

Smoky quartz is the national gem of Scotland, where it is known as Cairngorm. Large, well-formed crystals can grow to several hundred pounds in specific pocket environments. The color can be deepened through artificial irradiation or lightened through heating.

Field identification & locations

Identify in the field by its distinct grayish tint (not just surface dirt), hardness (it will scratch glass), and lack of cleavage. Common in granite-rich regions like the Alps, Brazil, and the Colorado Rockies. Often found alongside feldspar and mica.