metamorphic
Quartzite
Metamorphic Quartz Sandstone
Hardness of 7 on the Mohs scale, typically white, gray, pink, or reddish-brown due to iron oxide impurities. It has a vitreous to greasy luster, a non-foliated massive crystal structure with interlocking quartz grains, and conchoidal fracture with no true cleavage. Specific gravity ranges from 2.65 to 2.75.
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Physical properties
Hardness of 7 on the Mohs scale, typically white, gray, pink, or reddish-brown due to iron oxide impurities. It has a vitreous to greasy luster, a non-foliated massive crystal structure with interlocking quartz grains, and conchoidal fracture with no true cleavage. Specific gravity ranges from 2.65 to 2.75.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure, typically through tectonic compression in orogenic belts. The original quartz grains recrystallize along with the cementing material, forming a dense and remarkably durable interlocked mosaic of quartz crystals. Geological age can range from Precambrian to Cenozoic.
Uses & applications
Used extensively in construction as crushed stone for road bases, railroad ballast, and building facings, as well as in the production of silica refractory bricks and metallurgical fluxes.
Geological facts
Unlike ordinary sandstone, which breaks around the sand grains, quartzite fractures straight through the grains because the interlocking crystal structure is stronger than the grains themselves. Ancient stone age humans frequently utilized quartzite for making tools and projectile points due to its sharp conchoidal fracturing.
Field identification & locations
Can be identified in the field by its extreme hardness (it easily scratches glass and cannot be scratched by a knife) and the sugary texture of fractured surfaces where individual quartz crystals sparkle in the light. Found worldwide in mountainous regions and ancient cratons.
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