metamorphic
Weathered quartz-rich metamorphic rock
Likely quartzite or quartz-rich gneiss; exact identification requires a fresh surface and testing
AI-generated identification · may be incorrectComposed mainly of interlocking quartz with probable feldspar and mica; pale gray, tan, and brown from iron staining and weathering, with vitreous to dull luster. Quartz hardness is 7 Mohs; massive or weakly foliated texture, no obvious cleavage, and specific gravity about 2.6–2.7.
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Physical properties
Composed mainly of interlocking quartz with probable feldspar and mica; pale gray, tan, and brown from iron staining and weathering, with vitreous to dull luster. Quartz hardness is 7 Mohs; massive or weakly foliated texture, no obvious cleavage, and specific gravity about 2.6–2.7.
Formation & geological history
Likely formed when quartz-rich sandstone or silicate-rich crust was buried, heated, and recrystallized during regional metamorphism, generally hundreds of millions to billions of years ago. Surface browning reflects oxidation and prolonged weathering.
Uses & applications
Durable quartzite is used for landscaping, riprap, paving, aggregate, and building stone; attractive pieces may be collected as garden specimens, though this weathered example has limited lapidary value.
Geological facts
Quartzite commonly fractures across grains rather than around them and can be harder than steel tools. The apparent banding or streaking may indicate residual gneissic foliation rather than sedimentary layering.
Field identification & locations
Common in exposed metamorphic terrains worldwide, including the Appalachian, Rocky, and Precambrian shield regions. A glassy quartz-rich fresh break, resistance to scratching by a steel knife, and lack of fizz with dilute acid support quartzite; visible mica bands would favor gneiss.
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