metamorphic
Quartzite
Metamorphic Quartz Rock (SiO2)
Hardness of 7 on the Mohs scale, typically white to gray with red, brown, or pink iron-oxide stains, vitreous to greasy luster, massive to granular crystal structure, conchoidal fracture with poor cleavage, specific gravity of 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, typically white to gray with red, brown, or pink iron-oxide stains, vitreous to greasy luster, massive to granular crystal structure, conchoidal fracture with poor cleavage, specific gravity of 2.65.
Formation & geological history
Formed when quartz-rich sandstone or chert is subjected to high heat and pressure, usually through tectonic compression in orogenic belts. Can range in geological age from Precambrian to Cenozoic.
Uses & applications
Used in construction, railroad ballast, crushed stone for road surfaces, manufacturing of silica bricks, and occasionally as an ornamental stone or in decorative landscaping.
Geological facts
Pure quartzite is one of the most chemically inert and physically durable rocks on Earth, making it extremely resistant to weathering and erosion, which is why ridges formed of quartzite often stand out as high mountain crests.
Field identification & locations
Can be identified in the field by its extreme hardness (scratches glass easily), inability to be scratched by a knife, and the way it breaks across the quartz grains rather than around them, distinguishing it from sandstone.
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