metamorphic
Quartzite
Quartzite (Metamorphic Quartz Arenite)
Hardness: 7 on the Mohs scale, Color: Typically grey, white, or reddish-brown due to iron oxide impurities, Luster: Vitreous to greasy on fresh surfaces, Crystal Structure: Interlocking quartz crystals (non-foliated), Cleavage: None (fractures conchoidally through grains rather than around them), Specific Gravity: 2.65…
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Physical properties
Hardness: 7 on the Mohs scale, Color: Typically grey, white, or reddish-brown due to iron oxide impurities, Luster: Vitreous to greasy on fresh surfaces, Crystal Structure: Interlocking quartz crystals (non-foliated), Cleavage: None (fractures conchoidally through grains rather than around them), Specific Gravity: 2.65 - 2.70.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone or chert under high heat and pressure, typically during tectonic mountain-building events (orogenies). Geological age ranges from Precambrian to Cenozoic.
Uses & applications
Used in construction, road aggregate, railway ballast, manufacturing of silica brick and ferroalloys, decorative landscaping, and occasionally as dimension stone or countertops.
Geological facts
Because quartz is extremely resistant to weathering, quartzite mountains and ridges often stand out as prominent peaks or hogbacks in the landscape. It is so durable that it will scratch glass and cannot be easily scratched by a steel knife.
Field identification & locations
Can be identified in the field by testing hardness (scratches glass), observing that it does not fizz with dilute hydrochloric acid (distinguishing it from marble), and noting the sugary, interlocking texture of quartz grains on broken surfaces. Commonly found globally in ancient mountain belts and riverbeds.
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