igneous
Smoky Quartz in Matrix
Silicon dioxide (SiO2) within Pegmatite/Gneiss
Hardness: 7 (Mohs scale) for quartz; Color: Brown, smoky, translucent to opaque; Luster: Vitreous to greasy on crystal faces; Crystal Structure: Hexagonal (Trigonal); Cleavage: Indistinct/Conchoidal fracture; Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale) for quartz
- Color
- Brown, smoky, translucent to opaque
- Luster
- Vitreous to greasy on crystal faces
Identified More igneous →
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Physical properties
Hardness: 7 (Mohs scale) for quartz; Color: Brown, smoky, translucent to opaque; Luster: Vitreous to greasy on crystal faces; Crystal Structure: Hexagonal (Trigonal); Cleavage: Indistinct/Conchoidal fracture; Specific Gravity: 2.65.
Formation & geological history
Formed in late-stage cooling of magmatic pegmatites or in high-grade metamorphic environments. These crystals often grow within cavities or pockets of igneous rocks. The brown color is usually caused by natural gamma radiation activating aluminum impurities within the crystal structure.
Uses & applications
Commonly used as a decorative specimen for collectors, in landscaping, or processed into gemstones and beads for jewelry. When high-purity, quartz is used in electronics for its piezoelectric properties.
Geological facts
Smoky Quartz is the national gem of Scotland, where it is known as 'Cairngorm'. The dark color is unique because it is effectively a natural record of the rock's exposure to radiation over millions of years.
Field identification & locations
Identify by its ability to scratch glass and lack of cleavage. Look for the characteristic hexagonal prismatic points appearing from a host rock (matrix). Commonly found in mountainous regions with granitic outcrops like the Alps, Himalayas, or the Appalachian Mountains.
