metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale, color ranges from white and gray to pink or brown, vitreous to greasy luster, massive crystal structure with interlocking quartz grains, lacks distinct cleavage, specific gravity around 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, color ranges from white and gray to pink or brown, vitreous to greasy luster, massive crystal structure with interlocking quartz grains, lacks distinct cleavage, specific gravity around 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone or chert under high temperatures and tectonic pressures, typically taking millions of years in regional metamorphic environments.
Uses & applications
Used widely in construction, railroad ballast, decorative aggregate, dimension stone for countertops, and in manufacturing silica brick and ferrosilicon.
Geological facts
Quartzite is extremely durable and weather-resistant, which is why ridges formed of quartzite often persist as prominent hills or mountain ridges after surrounding softer rocks have eroded away.
Field identification & locations
Can be identified in the field by its inability to be scratched by steel (hardness 7), lack of effervescence with acid, and the way it breaks across the quartz grains rather than around them. Found globally in ancient mountain belts and river beds.
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