metamorphic
Quartzite
Quartzite (90%+ SiO2)
Hardness: 7 (Mohs scale), Color: Pinkish-red (from iron oxide), Luster: Vitreous to dull, Crystal Structure: Trigonal (granular texture), Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 7 (Mohs scale), Color: Pinkish-red (from iron oxide), Luster: Vitreous to dull, Crystal Structure: Trigonal (granular texture), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, where quartz grains recrystallize and fuse together. Often Proterozoic or Paleozoic in age.
Uses & applications
Used in construction as road ballast, railway ballast, and decorative stone. Sometimes used in glass manufacturing if pure.
Geological facts
Quartzite is so tough that it often survives erosion better than other rocks, forming prominent ridges and hilltops. It is harder than steel and will scratch a glass plate easily.
Field identification & locations
Identify by its extreme hardness and the fact that fractures break through the quartz grains rather than around them. Commonly found in riverbeds as rounded 'glacial' cobbles.
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