metamorphic
Quartzite
Quartzite (SiO2)
Hardness of 7 on Mohs scale; reddish-orange to yellowish-tan color due to iron oxide staining; glassy to greasy or dull luster; trigonal crystal system; no cleavage with conchoidal or uneven fracture; specific gravity approximately 2.65.
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Physical properties
Hardness of 7 on Mohs scale; reddish-orange to yellowish-tan color due to iron oxide staining; glassy to greasy or dull luster; trigonal crystal system; no cleavage with conchoidal or uneven fracture; specific gravity approximately 2.65.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone under extreme heat and pressure. The quartz grains recrystallize and interlock, forming a dense, hard metamorphic rock.
Uses & applications
Used as decorative stone, construction aggregate, railway ballast, and in crushed form for silica sand in glassmaking and refractory ceramics.
Geological facts
Quartzite is so tough and resistant to weathering that it often forms prominent ridges and hilltops. Unlike sandstone, when quartzite breaks, the fracture cuts through the quartz grains rather than along grain boundaries.
Field identification & locations
Identify by its hardness (scratches glass and steel easily), sugary to glassy texture, and lack of reaction to acid. Commonly found in mountainous regions, ancient metamorphic terrains, and river beds worldwide.
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