igneous
Weathered granitic cobble
Granitoid, likely granite or granodiorite
AI-generated identification · may be incorrectCoarse, mottled tan-gray rock with visible dark mica/amphibole and pale quartz/feldspar; likely Mohs 6–7, vitreous to dull luster, granular crystalline texture, and no obvious cleavage as a whole rock.
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Physical properties
Coarse, mottled tan-gray rock with visible dark mica/amphibole and pale quartz/feldspar; likely Mohs 6–7, vitreous to dull luster, granular crystalline texture, and no obvious cleavage as a whole rock.
Formation & geological history
An intrusive igneous rock that crystallized slowly from magma deep in Earth’s crust, commonly millions to billions of years old, then weathered and rounded in soil, stream gravel, or glacial sediment.
Uses & applications
Used as crushed aggregate, road stone, landscaping rock, building stone, and occasionally as a hand specimen; this small weathered cobble has little commercial value.
Geological facts
Granite-family rocks commonly contain quartz, potassium feldspar, plagioclase, and mica or amphibole. The brown surface coloration is likely iron-oxide weathering.
Field identification & locations
Identify it by its interlocking visible crystals and mottled quartz-feldspar-mica appearance; granite cobbles are widespread in continental terrains and river or glacial deposits. A fresh break or streak test would improve identification.
