metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale, colors range from white and gray to pink, red, or purple depending on impurities, vitreous to greasy luster, massive crystal structure with interlocking quartz grains, lack of visible cleavage, specific gravity of 2.65.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from white and gray to pink, red, or purple depending on impurities, vitreous to greasy luster, massive crystal structure with interlocking quartz grains, lack of visible cleavage, specific gravity of 2.65.
Formation & geological history
Formed from quartz-rich sandstone or chert through the processes of regional or contact metamorphism, involving high heat and pressure which causes the quartz grains to recrystallize and fuse tightly together. Geologically ancient, often dating back hundreds of millions of years.
Uses & applications
Used widely in construction for crushed stone, railroad ballast, dimension stone, wall tiles, decorative aggregates, and occasionally in the manufacture of silica brick and ferrosilicon.
Geological facts
Unlike parent sandstone, quartzite breaks across the quartz grains rather than around them, giving it an exceptionally tough and durable fracture. Famous occurrences include deposits in the Appalachian Mountains and the Baraboo Range in Wisconsin.
Field identification & locations
Identified easily by its extreme hardness (scratches glass easily and cannot be scratched by a knife blade) and the sugary, interlocking crystalline texture visible on freshly broken surfaces. Found worldwide in mountainous regions and old orogenic belts.
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