metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale. Color: White, gray, or tan, often with pinkish/reddish iron staining. Luster: Vitreous to waxy. Crystal Structure: Hexagonal (microcrystalline). Cleavage: Poor; characteristically breaks across grain boundaries with a conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale. Color: White, gray, or tan, often with pinkish/reddish iron staining. Luster: Vitreous to waxy. Crystal Structure: Hexagonal (microcrystalline). Cleavage: Poor; characteristically breaks across grain boundaries with a conchoidal fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse into a dense, interlocking matrix. Found in orogenic belts worldwide.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the manufacturing of glass and ceramics due to high silica content.
Geological facts
Quartzite is so tough that it often resists weathering better than other rocks, forming the caps of many prominent ridges and mountains. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and the way it fractures through the sand grains rather than around them. It typically has a sugary, crystalline appearance on fresh surfaces. Common in mountain ranges and ancient shields.
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