metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to grey, sometimes reddish or yellowish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); 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: White to grey, sometimes reddish or yellowish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, hard rock structure.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction, in the manufacture of glass and ceramics, and occasionally for primitive stone tools due to its hardness.
Geological facts
Quartzite is so durable that it often forms the crests of mountain ranges because it resists weathering more effectively than the rocks around it. It is often confused with marble, but can be distinguished because quartzite will scratch glass and does not fizz in acid.
Field identification & locations
Identify in the field by its extreme hardness and grainy, sandpaper-like texture that does not rub off. Common in mountainous regions and areas with ancient continental shields like the Appalachians or the Canadian Shield.
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