igneous
Granite Cobble
Granite (Porphyritic/Coarse-grained)
Hardness 6-7 on Mohs scale; phaneritic to porphyritic texture with light-colored feldspar phenocrysts, quartz, and dark biotite/amphibole minerals; dull to earthy weathered surface, glassy quartz specs; non-cleaving macroscopically as a rock, high density.
Identified More igneous →
Explore Granite Cobble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness 6-7 on Mohs scale; phaneritic to porphyritic texture with light-colored feldspar phenocrysts, quartz, and dark biotite/amphibole minerals; dull to earthy weathered surface, glassy quartz specs; non-cleaving macroscopically as a rock, high density.
Formation & geological history
Formed deep underground via the slow cooling and crystallization of felsic magma (plutonic igneous origin). Later exposed by erosion and rounded into a cobble by stream, river, or glacial transport.
Uses & applications
Used widely in construction as crushed stone, dimension stone, landscaping cobbles, river rock features, and aggregate for concrete.
Geological facts
Granite makes up a major portion of Earth's continental crust. Rounded granite cobbles like this one are often glacial erratics transported hundreds of miles during past ice ages.
Field identification & locations
Identified by its salt-and-pepper appearance with distinct interlocking visible crystals of feldspar, quartz, and dark mica or hornblende. Common in river beds, glacial till deposits, and mountain streams worldwide.
