metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale, colors range from white and gray to pink, brown, and yellowish due to iron oxide impurities. Luster is typically vitreous to greasy on fractured surfaces. Crystal structure is interlocking quartz grains, massive habit with no distinct cleavage.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from white and gray to pink, brown, and yellowish due to iron oxide impurities. Luster is typically vitreous to greasy on fractured surfaces. Crystal structure is interlocking quartz grains, massive habit with no distinct cleavage.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone or chert under high heat and tectonic pressure, typically during mountain-building events (orogenic processes) over hundreds of millions of years.
Uses & applications
Used heavily in construction for crushed stone, railroad ballast, roofing granules, and dimension stone, as well as in the manufacture of silica brick and metallurgical fluxes.
Geological facts
Because quartz is extremely resistant to weathering, quartzite ridges often form prominent resistant hills and mountain ridges standing above softer surrounding landscapes.
Field identification & locations
Can be identified in the field by its extreme hardness (scratches glass easily and cannot be scratched by a steel knife) and the way it breaks across the quartz grains rather than around them like sandstone. Found worldwide in ancient mountain belts.
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