metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone, where heat and pressure cause quartz grains to recrystallize and fuse together.
Uses & applications
Used in construction for road ballast, roofing granules, and decorative stone; also used in glass manufacturing and as a source of silica.
Geological facts
Quartzite is so durable that it often remains as ridges or peaks after softer surrounding rocks have eroded away. It is often harder than the steel of a geologist's hammer.
Field identification & locations
Identify by its hardness (will scratch glass) and granular, sugary appearance. Unlike sandstone, it breaks through the grains rather than around them. Common in mountain ranges worldwide.
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