metamorphic
Quartzite (likely iron-stained)
Quartzite; predominantly crystalline silicon dioxide (SiO₂)
AI-generated identification · may be incorrectUsually Mohs 7, pale gray to tan with vitreous to dull luster and massive, interlocking quartz grains; it lacks obvious cleavage and breaks irregularly. The specimen appears layered or flaky, so sandstone or quartz-rich schist is also possible from the image.
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Physical properties
Usually Mohs 7, pale gray to tan with vitreous to dull luster and massive, interlocking quartz grains; it lacks obvious cleavage and breaks irregularly. The specimen appears layered or flaky, so sandstone or quartz-rich schist is also possible from the image.
Formation & geological history
Forms when quartz-rich sandstone is recrystallized under heat and pressure during regional metamorphism, typically over millions to hundreds of millions of years. Common in mountain belts and Precambrian shield terrains.
Uses & applications
Used as crushed stone, aggregate, road material, building stone, countertops, and decorative slabs; attractive pieces are collected. Value is generally low unless unusually patterned or polished.
Geological facts
Quartzite is harder and more resistant to weathering than its sandstone precursor. Iron oxides commonly produce tan, yellow, or reddish coloration.
Field identification & locations
Look for a sugary crystalline texture, strong resistance to scratching by steel, and quartz-rich surfaces; sandstone feels more granular and may crumble. Common locations include the Appalachian Mountains, western United States, Brazil, India, and Scandinavia.
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