Smoky Quartz (with inclusions)

Physical Properties

Hardness: 7 on Mohs scale; Color: Gray, brownish-black, translucent to semi-opaque; Luster: Vitreous to greasy on fracture surfaces; Crystal Structure: Trigonal (hexagonal prisms); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & Geological History

Formed in igneous and metamorphic environments, specifically pegmatites and hydrothermal veins. The smoky color is caused by natural irradiation of aluminum-bearing quartz over millions of years.

Uses & Applications

Used in gemstone jewelry, ornamental carvings, and as a popular specimen for mineral collectors. Some industrial uses include pressure sensors due to piezoelectric properties.

Geological Facts

Smoky quartz is the national gem of Scotland, where it is known as 'Cairngorm.' The color can range from a light yellowish gray to a black so dark it is nearly opaque.

Field Identification & Locations

Identify in the field by its hardness (will scratch glass), lack of cleavage, and characteristic smoky translucency. Commonly found in mountainous regions like the Alps, Brazil, and the United States (Colorado).

Identified on: 4/27/2026

Mode: Standard