metamorphic
Quartzite
Quartzite (predominantly Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or clouded blue/grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or clouded blue/grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or clouded blue/grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); 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 and fuse together into a dense, hard rock.
Uses & applications
Used in construction as crushed stone for road ballast, as a decorative building stone, and in the manufacturing of glass and ceramics due to high silica content.
Geological facts
Quartzite is so tough that it often breaks through the individual quartz grains rather than around them, which distinguishes it from sandstone. Some varieties are billions of years old.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Commonly found in folded mountain ranges across North America, Europe, and Brazil.
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