metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Pink, reddish-brown, or grey; Luster: Vitreous to dull; Crystal structure: Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Pink, reddish-brown, or grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pink, reddish-brown, or grey; Luster: Vitreous to dull; Crystal structure: Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together, often in Precambrian or Paleozoic geological environments.
Uses & applications
Used in construction as crushed stone for roadbeds, railway ballast, and as a decorative stone in architecture and landscaping. Also used in glass making if high purity.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks, forming distinctive ridges and resistant mountain peaks. It will scratch glass easily, unlike the sandstone from which it originated.
Field identification & locations
Identify by its granular but smooth 'sugary' texture and extreme hardness. Often found in glaciated areas as rounded cobbles or in massive mountain formations. Common in the Appalachian Mountains and the Great Lakes region.
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