metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (scratches glass). Color: White to light grey. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal or irregular fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- White to light grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (scratches glass). Color: White to light grey. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None (conchoidal or irregular fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, interlocking mosaic.
Uses & applications
Used heavily in construction as road ballast, roofing granules, and dimension stone for flooring and walls. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the peaks of mountain ranges and ridges.
Field identification & locations
Identify in the field by its extreme hardness (it will not be scratched by a steel knife) and its sugary, crystalline texture that breaks across grain boundaries rather than around them. Commonly found in folded mountain belts.
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