metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: Tan, beige, white, or light pink. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.63-2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, white, or light pink
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, beige, white, or light pink. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.63-2.65.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, creating a much harder rock. Most are Precambrian or Paleozoic in age.
Uses & applications
Extensively used in construction as crushed stone for road gravel and railway ballast. Due to its hardness, it is also used as dimension stone in architecture (slabs, flooring) and as a source for industrial silica.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is more resistant to weathering than the original sandstone it formed from, often creating prominent ridges and hills in the landscape.
Field identification & locations
Identify by its extreme hardness and grainy texture that looks like sandstone but breaks through individual grains rather than around them. Often found in mountainous regions or ancient shield areas; commonly found in riverbeds as rounded cobbles.
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