metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale), Color: light gray to white with sugary texture, Luster: vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: none, fracture: conchoidal/irregular.
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Physical properties
Hardness: 7 (Mohs scale), Color: light gray to white with sugary texture, Luster: vitreous to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: none, fracture: conchoidal/irregular.
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure during regional metamorphism, leading to the recrystallization of quartz grains into a dense, interlocking matrix.
Uses & applications
Used extensively in road construction, as railroad ballast, in glass manufacturing, and as decorative stone in landscaping or architectural cladding.
Geological facts
Quartzite is so durable that it often survives intense weathering better than the rocks around it, creating prominent ridges or hills. It is often confused with marble but is significantly harder.
Field identification & locations
Identify by its ability to scratch glass and its granular, sugary appearance when freshly broken. Common in fold mountain belts and areas of ancient continental crust like the Appalachians or the Alps.
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