metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or glassy with mottled texture; Luster: Vitreous to waxy; Structure: Crystalline mosaic (granoblastic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or glassy with mottled texture
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or glassy with mottled texture; Luster: Vitreous to waxy; Structure: Crystalline mosaic (granoblastic); 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 original quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used as a decorative stone, in construction as crushed stone or railway ballast, for floor tiling, countertops, and historically as a tool stone because of its hardness.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in mountainous areas, forming prominent ridges and peaks. It is often confused with marble, but quartzite is much harder and will not react with acid.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It often has a distinctive sugary or grainy appearance under a lens. Commonly found in folded mountain belts and ancient shield areas like the Appalachians or the Great Lakes region.
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