metamorphic
Quartzite
Quartzite (predominantly SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, 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
- Gray, white, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic.
Uses & applications
Used as building stone, decorative paving, crushed stone for road construction, and occasionally in glass manufacturing if pure enough.
Geological facts
Quartzite as a rock is so tough that it often breaks through the quartz grains rather than along their boundaries, unlike the sandstone it originated from.
Field identification & locations
Identify by its extreme hardness (it will scratch glass and steel) and its grainy but fused appearance. Commonly found in folded mountain belts and ancient shield areas.
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