metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to light grey; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to light grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light grey; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. Found in orogenic belts worldwide, ranging from millions to billions of years old.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone; used in industrial manufacturing for glass, ceramics, and as a source of silica; popular as a landscaping stone.
Geological facts
Quartzite is so tough that it often survives erosion better than the surrounding rocks, frequently forming the caps of ridges and mountains. It is harder than a steel knife and will scratch glass easily.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a knife) and its grainy, sugary texture. Unlike sandstone, it will break through the quartz grains rather than around them. Common in mountainous regions/shield areas.
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