metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale, colors range from white and gray to pink, brown, and reddish due to iron oxide impurities. Luster is vitreous to greasy on fractured surfaces. Crystal structure is interlocking quartz grains, massive and non-foliated. No true cleavage, breaks with a conchoidal fracture.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from white and gray to pink, brown, and reddish due to iron oxide impurities. Luster is vitreous to greasy on fractured surfaces. Crystal structure is interlocking quartz grains, massive and non-foliated. No true cleavage, breaks with a conchoidal fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone or chert under high temperatures and tectonic pressures, often during mountain-building events over millions of years.
Uses & applications
Used in construction, as crushed stone for road bases, in the production of railroad ballast, for manufacturing refractory bricks, and occasionally as decorative stone or countertops.
Geological facts
Because quartz is extremely resistant to weathering, quartzite ridges often form prominent, durable mountain crests and resistant hills in eroded landscapes.
Field identification & locations
Can be identified in the field by its inability to be scratched by a steel knife (Mohs hardness 7), its sugary texture on broken surfaces, and the fact that it breaks through the quartz grains rather than around them (unlike sandstone). Found globally in ancient mountain belts and shield areas.
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