metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or pale pink; 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 pale pink
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or pale pink; 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 or contact metamorphism of quartz sandstone. Intense heat and pressure cause the individual quartz grains to recrystallize and fuse together into a dense, hard rock mass.
Uses & applications
Used as a decorative stone in construction, for railway ballast, as a raw material for glass and ceramics, and in the production of ferrosilicon.
Geological facts
Quartzite is so durable that it often forms the crests of ridges and mountains because it resists weathering better than surrounding rocks. It is distinct from sandstone because it breaks through the grains rather than around them.
Field identification & locations
Identify by its extreme hardness (scratches glass) and its sugary, crystalline texture. It is commonly found in mountain belts worldwide such as the Appalachians or the Alps.
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