metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white, grey, or reddish (due to iron oxide); Luster: vitreous to dull; Crystal structure: hexagonal (within grains); Cleavage: none, breaks with conchoidal or irregular fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white, grey, or reddish (due to iron oxide)
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white, grey, or reddish (due to iron oxide); Luster: vitreous to dull; Crystal structure: hexagonal (within grains); Cleavage: none, breaks with conchoidal or irregular fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically in convergent plate boundaries. The original quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used as crushed stone for road construction and railway ballast; decorative stone for countertops, walls, and flooring; used in glass making and metallurgy if high purity silica.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is much harder and more resistant than the sandstone from which it originated, often forming prominent ridges in mountain ranges.
Field identification & locations
Identify by its extreme hardness and grainy, sugary texture. Unlike marble, it will not fizz when exposed to acid. Commonly found in folded mountain belts globally, such as the Appalachians or the Alps.
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