metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be tan or brownish due to impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be tan or brownish due to impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. It can be found in mountain belts worldwide formed during tectonic plate collisions.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the manufacturing of glass and ceramics due to its high silica content.
Geological facts
Quartzite is so hard and durable that it often forms the ridges and peaks of mountain ranges because it resists weathering better than the surrounding rock types.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, granular texture. Unlike sandstone, it breaks across the quartz grains rather than around them. Found globally in ancient mountain cores.
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