metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Pink, reddish-brown, or grey; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6 - 2.7
- Hardness
- 7 on Mohs scale
- Color
- Pink, reddish-brown, or grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pink, reddish-brown, or grey; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6 - 2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse into a dense rock matrix. It can range from Precambrian to much younger geological ages.
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. High-purity quartzite is also a source of silica for glassmaking and industrial silicon production.
Geological facts
Quartzite is so durable that it often forms the tops of hills and ridges because it resists weathering better than the surrounding rock. It breaks across the quartz grains rather than around them, which distinguishes it from sandstone.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass) and its sugary, crystalline texture. It is commonly found in mountain belts worldwide, such as the Appalachians or the Alps.
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