metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: White to light grey with a sugary/crystalline appearance, Luster: Vitreous to dull, Crystal Structure: Trigonal (as individual grains), Cleavage: None/Conchoidal fracture. Extremely durable and resistant to scratching.
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Physical properties
Hardness: 7 (Mohs scale), Color: White to light grey with a sugary/crystalline appearance, Luster: Vitreous to dull, Crystal Structure: Trigonal (as individual grains), Cleavage: None/Conchoidal fracture. Extremely durable and resistant to scratching.
Formation & geological history
Formed primarily from the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse into an interlocking network of crystals. Often found in Precambrian or Paleozoic geological formations.
Uses & applications
Used extensively in construction as crushed stone or road ballast, as a dimension stone for flooring and countertops, and in industrial manufacturing as a source of silica for glass and ceramics.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it resists weathering much better than the rocks surrounding it. Unlike sandstone, quartzite breaks through the sand grains rather than around them.
Field identification & locations
Can be identified in the field by its inability to be scratched by a steel blade (unlike marble) and its lack of reaction to acid. It often presents a grainy, 'sugary' texture. Common in Appalachian and Rocky Mountain regions.
