metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: White, gray, or tan with yellowish staining from iron. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White, gray, or tan with yellowish staining from iron
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: White, gray, or tan with yellowish staining from iron. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, creating an extremely hard, dense rock.
Uses & applications
Used in construction as crushed stone for road gravel and railway ballast, as a dimension stone for flooring or countertops, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the resistant caps of mountain ranges like the Appalachians.
Field identification & locations
Identify in the field by its hardness (it easily scratches glass) and its sugary texture where broken. Unlike sandstone, which breaks around grains, quartzite breaks through the grains. Found worldwide in metamorphic belts.
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