igneous
Weathered granite or granitic gneiss cobble
Quartz–feldspar–mica granitic rock; possibly gneissic granite
AI-generated identification · may be incorrectCoarse, mottled gray, cream, and black fabric with visible quartz/feldspar and dark biotite or amphibole; granular, nonmetallic luster, massive to weakly foliated texture, Mohs hardness about 6–7, and no obvious cleavage as a whole rock.
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Physical properties
Coarse, mottled gray, cream, and black fabric with visible quartz/feldspar and dark biotite or amphibole; granular, nonmetallic luster, massive to weakly foliated texture, Mohs hardness about 6–7, and no obvious cleavage as a whole rock.
Formation & geological history
Formed by slow crystallization of silica-rich magma deep in the crust, likely during Precambrian to younger continental crust formation; rounded shape and surface alteration indicate prolonged stream or glacial transport and weathering.
Uses & applications
Commonly used as crushed aggregate, road stone, building stone, landscaping rock, and ornamental cobbles; this specimen has modest collector value unless provenance or unusual texture is documented.
Geological facts
The pale zones are likely weathered feldspar or quartz-rich patches, while dark grains are ferromagnesian minerals. Granitic rocks commonly contain interlocking crystals that make them durable but difficult to break.
Field identification & locations
Identify it by its speckled quartz–feldspar–dark-mineral composition, hard surface, and lack of layering; a streak test is usually white, and dilute acid should not fizz unless carbonate veins are present. Common worldwide in continental shields and mountain belts.
