metamorphic
Quartzite
Quartzite (Metamorphic rock primarily composed of SiO2)
Hardness: 7 on the Mohs scale; Color: Typically white to gray, but can be pink, red, or yellow due to iron impurities; Luster: Vitreous to greasy on fractured surfaces; Crystal structure: Non-foliated, interlocking mosaic of quartz crystals; Cleavage: None, typically fractures conchoidally; Specific gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Luster
- Vitreous to greasy on fractured surfaces
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Physical properties
Hardness: 7 on the Mohs scale; Color: Typically white to gray, but can be pink, red, or yellow due to iron impurities; Luster: Vitreous to greasy on fractured surfaces; Crystal structure: Non-foliated, interlocking mosaic of quartz crystals; Cleavage: None, typically fractures conchoidally; Specific gravity: 2.65.
Formation & geological history
Formed when quartz-rich sandstone or chert is subjected to high temperatures and pressures usually associated with tectonic compression in orogenic belts. The original quartz grains recrystallize along with the cementing material.
Uses & applications
Used in construction, as crushed stone for road bases, railway ballast, dimension stone, and in manufacturing silica brick and ferrosilicon.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why ridges formed by quartzite often remain as prominent hills or mountain ridges (such as quartzites in the Appalachian Mountains).
Field identification & locations
Can be identified in the field by its hard, non-foliated nature and the fact that it will scratch glass easily. Unlike sandstone, quartzite fractures across the individual grains rather than around them.
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