mineral

Smoky Quartz with Chert

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Gray to black and translucent; Luster: Vitreous to waxy; Crystal structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray to black and translucent
Luster: Vitreous to waxy

Identified June 22, 2026More mineral →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray to black and translucent; Luster: Vitreous to waxy; Crystal structure: Hexagonal/Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Smoky quartz typically forms in igneous rocks like pegmatites or hydrothermal veins where silicon dioxide is subjected to natural radiation from surrounding minerals. Chert forms through the accumulation of silica-rich microfossils or precipitation from hydrothermal fluids in sedimentary or volcanic environments.

Uses & applications

Used as a gemstone in jewelry, as a healing crystal in metaphysical practices, and as a common specimen for mineral collectors. Some industrial quartz is used in timepiece oscillators.

Geological facts

The smoky color is caused by free silicon formed from silicon dioxide by natural irradiation. It is the national gem of Scotland, where it is often called Cairngorm.

Field identification & locations

Identify by its characteristic 7 hardness (cannot be scratched by steel), conchoidal fracture, and smoky translucency. Often found in pockets of Granite or as nodules in volcanic host rock.