metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan staining; Luster: vitreous to dull; Crystal structure: hexagonal/trigonal (as microcrystalline quartz); Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, often with yellow or tan staining
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan staining; Luster: vitreous to dull; Crystal structure: hexagonal/trigonal (as microcrystalline quartz); Cleavage: none (fractures conchoidally); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together into a dense, hard rock. This specimen appears to be from a continental crust environment.
Uses & applications
Used as crushed stone for road construction and railway ballast; decorative stone in landscaping; historically used for making primitive stone tools due to its hardness and fracture pattern.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, leading to the formation of ridges and mountaintops. It is often confused with marble, but unlike marble, it will not fizz in acid and can scratch glass.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that has been fused into a sugary appearance. Commonly found in folded mountain belts and ancient cratons.
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