metamorphic
Quartzite
Metamorphic Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan to iron-stained orange with translucent white interior; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None/Conchoidal fracture; Specific gravity: 2.63-2.65
- Hardness
- 7 on Mohs scale
- Color
- Tan to iron-stained orange with translucent white interior
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to iron-stained orange with translucent white interior; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None/Conchoidal fracture; Specific gravity: 2.63-2.65
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the individual sand grains to recrystallize and fuse together into a dense, interlocking matrix.
Uses & applications
Extensively used in construction as road ballast, railway ballast, and decorative stone. High-purity quartzite is used to produce glass, silicon metal, and ferrosilicon for electronics and metallurgy.
Geological facts
Quartzite is so durable that it often forms the crests of high ridges and mountains, as it resists weathering much better than the rocks surrounding it. It is one of the hardest natural building materials available.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Unlike sandstone, quartzite breaks through the grains rather than around them, which results in a smooth, crystalline fracture surface.
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