metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be yellowish or tan due to impurities; Luster: vitreous to greasy; Crystal Structure: Trigonal (as quartz grains); Cleavage: None/Conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be yellowish or tan due to impurities; Luster: vitreous to greasy; Crystal Structure: Trigonal (as quartz grains); Cleavage: None/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 together, creating a dense, interlocking matrix.
Uses & applications
Used widely in construction as road ballast, decorative stone, and flooring. It is also used as raw material in the glass and ceramics industries due to high silica content.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and mountains as surrounding softer rocks wear away. It will scratch glass easily.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (cannot be scratched by a steel knife). Unlike marble, it will not fizz when exposed to acid. Commonly found in folded mountain belts globally.
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