metamorphic
Quartzite
Metamorphic Quartzite (primarily SiO2)
Hardness: 7 on the Mohs scale, Color: Typically white to gray, can also be pink, red, or yellow due to impurities, Luster: Vitreous to greasy, Crystal structure: Trigonal (microcrystalline/interlocking quartz grains), Cleavage: None (fractures conchoidally), Specific gravity: 2.65
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Physical properties
Hardness: 7 on the Mohs scale, Color: Typically white to gray, can also be pink, red, or yellow due to impurities, Luster: Vitreous to greasy, Crystal structure: Trigonal (microcrystalline/interlocking quartz grains), Cleavage: None (fractures conchoidally), Specific gravity: 2.65
Formation & geological history
Formed from quartz-rich sandstone or chert under high temperature and pressure conditions associated with tectonic compression during regional metamorphism.
Uses & applications
Used in construction, as crushed stone for road foundations, railway ballast, manufacturing of silica brick, and sometimes as a decorative stone or in countertops.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why ridges made of quartzite often form prominent mountain ranges.
Field identification & locations
Can be identified in the field by its high hardness (scratches glass easily, cannot be scratched by a knife) and the way it breaks across the quartz grains rather than around them, unlike sandstone.
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