igneous
Granite-like cobble
Granitoid, likely biotite granite or granodiorite
AI-generated identification · may be incorrectCoarse-grained, speckled gray-beige rock with quartz, feldspar, and dark biotite/amphibole; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no obvious cleavage as a whole rock. Exact identification is limited by the photograph.
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Physical properties
Coarse-grained, speckled gray-beige rock with quartz, feldspar, and dark biotite/amphibole; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no obvious cleavage as a whole rock. Exact identification is limited by the photograph.
Formation & geological history
Formed when silica-rich magma cooled slowly deep in the crust, producing visible crystals; commonly Precambrian to Mesozoic in age, depending on source. Its rounded shape indicates later transport by stream or glacial action.
Uses & applications
Used as crushed stone, aggregate, road material, dimension stone, and decorative landscaping rock; attractive pieces may be polished, though this specimen is mostly a common field cobble.
Geological facts
Quartz appears glassy gray, feldspar is pale, and biotite or amphibole creates dark flecks. Granodiorite generally contains more plagioclase than potassium feldspar and may look similar.
Field identification & locations
Common in continental crust and glacial deposits worldwide, especially regions underlain by granite batholiths. A fresh surface, acid test, hand lens, and hardness test would help distinguish granite from gneiss or weathered volcanic rock.
