metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Typically white to gray, though impurities create pink, red, or green tints; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal systems; Specific gravity: 2.6–2.7.
- Hardness
- 7 (Mohs scale)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Typically white to gray, though impurities create pink, red, or green tints; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal systems; Specific gravity: 2.6–2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz sandstone. High pressure and temperature cause the sand grains to recrystallize and fuse into a dense, interlocking matrix. This process can occur over millions of years during mountain-building events.
Uses & applications
Used extensively in construction as crushed stone for road beds and railway ballast, in architecture as flooring or wall cladding, and in industrial glass making or as an abrasive.
Geological facts
Quartzite is so tough that it often outlasts surrounding bedrock, forming prominent ridges and hills. It is harder than steel and will scratch a glass plate easily.
Field identification & locations
Identify in the field by its superior hardness (cannot be scratched by a knife) and sugary, granular texture. Unlike sandstone, when broken, quartzite fractures through the grains rather than around them. Common in folded mountain ranges globally.
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