metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White, grey, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White, grey, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, grey, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events. The original quartz grains recrystallize into an interlocking mosaic of crystals.
Uses & applications
Used as decorative stone in architecture, railway ballast, road construction, and as a source of silica for glass manufacturing and electronics.
Geological facts
Quartzite is so durable that it often forms the ridges and peaks of mountain ranges because it resists weathering better than the surrounding rocks. One famous formation is the Baraboo Quartzite in Wisconsin.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and granular, sugary appearance. Unlike sandstone, it breaks across the grains rather than around them.
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