metamorphic
Quartz-rich metamorphic rock, likely quartzite
Quartzite, composed predominantly of quartz (SiO₂), with minor iron-oxide staining and possible feldspar/mica
AI-generated identification · may be incorrectTypically Mohs hardness 7, white to gray with yellow-brown limonite staining, and a vitreous to sugary luster. Quartz grains are tightly interlocked; it lacks obvious cleavage and breaks irregularly, though this weathered specimen may resemble quartz-rich sandstone.
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Physical properties
Typically Mohs hardness 7, white to gray with yellow-brown limonite staining, and a vitreous to sugary luster. Quartz grains are tightly interlocked; it lacks obvious cleavage and breaks irregularly, though this weathered specimen may resemble quartz-rich sandstone.
Formation & geological history
Forms when quartz-rich sandstone is recrystallized under elevated heat and pressure during regional metamorphism, commonly in Precambrian to Paleozoic mountain belts. The rusty colors result from oxidation of iron-bearing impurities near the surface.
Uses & applications
Crushed quartzite is used for aggregate, road stone, silica, and occasionally architectural facing stone; attractive pieces are collected but are generally not used as gemstones.
Geological facts
A useful diagnostic feature is that quartzite fractures through grains rather than around them, making it harder and more resistant than sandstone. Strong effervescence with dilute acid would suggest carbonate cement and argue against pure quartzite.
Field identification & locations
Common in metamorphic mountain regions worldwide, including the Appalachian, Rocky, and Scandinavian belts. Test hardness against glass and inspect a fresh break: abundant interlocking quartz and no visible sedimentary layering support quartzite.
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