metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but pinkish, reddish, or tan due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; 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 pinkish, reddish, or tan due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the quartz grains to recrystallize and fuse together into a dense, crystalline rock.
Uses & applications
Used in construction for road ballast, roofing granules, and as a dimension stone for flooring and walls; also used in the manufacture of glass and silicon.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks and forms high ridges or resistant cliffs. It is much harder and more durable than the parent sandstone from which it originated.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and the way it breaks through quartz grains rather than around them, unlike sandstone. Common in mountainous regions with folded rock layers.
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