metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, white, gray; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with conchoidal or irregular fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, white, gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, white, gray; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with conchoidal or irregular fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together.
Uses & applications
Used in construction as crushed stone, road ballast, decorative building stone, and historically as a tool stone for making sharp edges (similar to flint).
Geological facts
Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the tops of ridges and hills. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify by its extreme hardness and grainy, sandpaper-like surface that does not crumble. Commonly found in mountainous regions or ancient shield areas. Tips: Look for a sugary texture on fresh breaks.
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