gemstone
Smoky Quartz
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Grayish-brown to black; Luster: Vitreous (glassy); Crystal structure: Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Grayish-brown to black
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 7 (Mohs scale); Color: Grayish-brown to black; Luster: Vitreous (glassy); Crystal structure: Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Smoky quartz forms in igneous and metamorphic rocks, particularly granite pegmatites. The smoky color is caused by natural radiation from surrounding rocks acting on aluminum impurities within the quartz crystal lattice.
Uses & applications
Commonly used in jewelry (faceting, beads), carving, and as a popular collector's mineral specimen. Historically used in the first sunglasses in 12th century China.
Geological facts
The brown color is unstable at high temperatures; heating smoky quartz can turn it yellow (citrine) or colorless. Large, well-formed crystals are common in the Swiss Alps and Colorado.
Field identification & locations
Identified by its transparency and distinct smoky brown hue. In the field, it is often found in quartz veins or pockets within granite. Collectors look for clarity, uniform color, and sharp facet edges.
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