metamorphic
Quartzite
Quartzite (chiefly SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often brownish/tan due to impurities; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline masses); Cleavage: none, breaks with conchoidal fracture.
- 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, often brownish/tan due to impurities; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline masses); Cleavage: none, breaks with conchoidal fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic compression cause the sand grains to recrystallize and fuse into a solid network.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone. High-purity quartzite is used to produce silica sand for glassmaking and metallurgy.
Geological facts
Quartzite is so tough that it often outlasts surrounding rocks through erosion, forming the caps of many ridges and mountains. It is harder than a steel knife blade and will easily scratch glass.
Field identification & locations
Identify by its extreme hardness and the way it breaks through the sand grains rather than around them (unlike sandstone). Found globally in mountainous regions and ancient shield areas.
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