metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale. Color ranges from white and gray to pink, red, or purple due to iron oxides. Luster is vitreous to greasy on fractured surfaces. Crystal structure is a dense interlocking network of quartz grains. Cleavage is absent (it fractures conchoidally). Specific gravity is around 2.65.
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Physical properties
Hardness of 7 on the Mohs scale. Color ranges from white and gray to pink, red, or purple due to iron oxides. Luster is vitreous to greasy on fractured surfaces. Crystal structure is a dense interlocking network of quartz grains. Cleavage is absent (it fractures conchoidally). Specific gravity is around 2.65.
Formation & geological history
Formed from quartz-rich sandstone or chert under high temperatures and pressures associated with tectonic compression during regional metamorphism.
Uses & applications
Used in construction, as crushed stone for road building, in railroad ballast, and for manufacturing ferrosilicon, silica brick, and tiles.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why ridges formed of quartzite often persist as high mountain crests or hills.
Field identification & locations
Can be identified in the field by its hardness (scratches glass easily), inability to be scratched by a knife, lack of effervescence with acid, and the sugary texture of interlocking quartz grains visible on fresh fractures. Found worldwide in ancient mountain belts.
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