igneous
Weathered quartz-rich cobble
Likely quartzite or quartz-rich granitic rock; exact identification is uncertain from the image
AI-generated identification · may be incorrectTan to gray, rounded and strongly weathered, with a vitreous to dull luster and granular texture. Quartzite typically has Mohs hardness 7 and no cleavage; granite-derived material contains quartz, feldspar, and minor mica, with hardness about 6–7.
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Physical properties
Tan to gray, rounded and strongly weathered, with a vitreous to dull luster and granular texture. Quartzite typically has Mohs hardness 7 and no cleavage; granite-derived material contains quartz, feldspar, and minor mica, with hardness about 6–7.
Formation & geological history
Likely a glacially or fluvially transported cobble shaped by abrasion and surface weathering; its original rock may be Precambrian or younger depending on source terrain.
Uses & applications
Usually valued as a natural landscaping or educational specimen; quartzite is also used as aggregate, building stone, and decorative material.
Geological facts
The rounded form indicates transport, while the tan rind likely reflects iron-oxide staining and weathering. A fresh broken surface would best distinguish quartzite from granite or other quartz-rich rocks.
Field identification & locations
Common in river gravels, glacial deposits, beaches, and crushed-rock surfaces. Test for abundant interlocking quartz grains, lack of visible feldspar cleavage, and resistance to scratching by steel; acid testing is generally uninformative.
