metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or tan (often yellowish/brown from iron oxide staining); Luster: Vitreous to greasy; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or tan (often yellowish/brown from iron oxide staining); Luster: Vitreous to greasy; Crystal structure: Trigonal/Hexagonal (microcrystalline); 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 individual quartz grains to recrystallize and fuse together into a dense, interlocking mosaic.
Uses & applications
Used as a decorative stone in construction, road ballast, manufacture of glass and ceramics, and as a durable material for countertops and flooring.
Geological facts
Quartzite is so tough that it often survives intense erosion to form the crests of mountain ridges. Unlike sandstone, when quartzite is broken, it fractures through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and its granular, sugary texture. Found globally in mountainous regions and areas of intense tectonic activity.
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