metamorphic
Quartzite
Metamorphic Quartz Arenite (SiO2)
Hardness of 7 on the Mohs scale, predominantly white or milky color with occasional yellowish-brown iron oxide staining, vitreous to greasy luster, massive to granular crystal structure, conchoidal fracture with indistinct cleavage, and a specific gravity of around 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, predominantly white or milky color with occasional yellowish-brown iron oxide staining, vitreous to greasy luster, massive to granular crystal structure, conchoidal fracture with indistinct cleavage, and a specific gravity of around 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone or chert under intense heat and tectonic pressure, transforming the loosely bound sand grains into an interlocking, highly durable mosaic of quartz crystals over millions of years.
Uses & applications
Used heavily in construction as crushed stone for road bases, railway ballast, dimension stone, roofing granules, and in industrial applications such as the manufacture of refractory bricks and ferrosilicon.
Geological facts
Quartzite is so durable that weathering-resistant ridges formed by quartzite layers often stand out as prominent mountain crests and hills, such as the Baraboo Range in Wisconsin.
Field identification & locations
Can be identified in the field by its extreme hardness (it will easily scratch glass and cannot be scratched by a steel knife) and the characteristic sugary, interlocking crystalline texture visible on freshly broken surfaces, contrasting with sandstones which tend to crumble into individual grains.
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