metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness of 7 on Mohs scale; light grey, pinkish, to reddish-brown coloration due to iron oxide inclusions; vitreous to dull luster; granoblastic interlocking quartz grain texture; lacks cleavage; specific gravity ~2.65.
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Physical properties
Hardness of 7 on Mohs scale; light grey, pinkish, to reddish-brown coloration due to iron oxide inclusions; vitreous to dull luster; granoblastic interlocking quartz grain texture; lacks cleavage; specific gravity ~2.65.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone, where intense heat and pressure cause quartz grains to recrystallize into a dense, interlocking matrix.
Uses & applications
Used in lapidary work, decorative stone cabochons, construction aggregate, railway ballast, and dimension stone.
Geological facts
Quartzite is extremely tough and weather-resistant; unlike sandstone, when quartzite breaks, it fractures through the quartz grains rather than around them.
Field identification & locations
Can be identified in the field by its scratch resistance (scratches glass easily), sugary/granular fused appearance, and smooth pebble form when stream-worn or polished. Commonly found in ancient mountain belts and river gravel deposits.
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