metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, white with yellowish banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, white with yellowish banding
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, white with yellowish banding; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); 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 into an interlocking mosaic. Found in orogenic belts worldwide.
Uses & applications
Used as crushed stone for road construction and railway ballast; decorative landscape stone; architectural stone; and occasionally as a gemstone in tumbled form.
Geological facts
Quartzite is so hard that when it breaks, the fracture goes through the individual quartz grains rather than around them, distinguishing it from sandstone. Many river rocks are quartzite due to its extreme resistance to erosion.
Field identification & locations
Identify by its hardness (it will easily scratch glass) and its sugary, crystalline texture under a lens. Commonly found in riverbeds and glacial deposits across North America and Europe.
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