metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to grey, often with tan or reddish brown staining; Luster: vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to grey, often with tan or reddish brown staining; Luster: vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: none (conchoidal 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 original quartz sand grains to recrystallize and fuse together into a dense, hard interlocking network.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and decorative building stone. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often survives intense weathering better than other rocks, frequently forming the tops of ridges and resistant mountain peaks. It will scratch glass easily.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture that breaks across the grains rather than around them (unlike sandstone). Commonly found in folded mountain belts.
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