metamorphic
Quartzite
Quartzite; predominantly recrystallized quartz (SiO₂), with minor iron-oxide and other impurities
AI-generated identification · may be incorrectTypically very hard (Mohs 7), pinkish to reddish-brown, granular and glassy to dull, with interlocking quartz crystals and no obvious cleavage; specific gravity about 2.6–2.7. The specimen appears fine- to medium-grained and iron-stained.
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Physical properties
Typically very hard (Mohs 7), pinkish to reddish-brown, granular and glassy to dull, with interlocking quartz crystals and no obvious cleavage; specific gravity about 2.6–2.7. The specimen appears fine- to medium-grained and iron-stained.
Formation & geological history
Formed when quartz-rich sandstone was subjected to intense heat and pressure, causing quartz grains to recrystallize and fuse; ages vary from Precambrian to younger mountain-building events. Common in metamorphic belts and resistant mountain ridges.
Uses & applications
Used as crushed stone, road aggregate, architectural stone, countertops, and decorative carvings; attractive pink varieties are collected but are generally not gem-grade.
Geological facts
Quartzite commonly fractures across original sandstone grains rather than around them, making it tougher than sandstone. Pink or red coloration usually reflects hematite or other iron oxides.
Field identification & locations
Field identification: scratches glass, feels exceptionally hard, and shows fused quartz grains; unlike sandstone, it does not readily crumble along grain boundaries. Common worldwide, including the Appalachians, Rocky Mountains, India, Brazil, and Scandinavia.
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