igneous
Red granite or granitic gneiss cobble
Quartz–feldspar–mica rock; likely granite, possibly gneiss
AI-generated identification · may be incorrectCoarse, mottled reddish-brown and gray rock with visible quartz, pink potassium feldspar, dark biotite or amphibole, and possible foliation. Typical hardness is about 6–7 Mohs; granular texture, vitreous quartz luster, and no obvious cleavage as a whole rock.
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Physical properties
Coarse, mottled reddish-brown and gray rock with visible quartz, pink potassium feldspar, dark biotite or amphibole, and possible foliation. Typical hardness is about 6–7 Mohs; granular texture, vitreous quartz luster, and no obvious cleavage as a whole rock.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic intrusive events; gneiss forms when such rock is metamorphosed under high heat and pressure. The rounded shape indicates transport by water or glacial action.
Uses & applications
Used as crushed aggregate, dimension stone, paving, monuments, and decorative landscaping material; attractive polished pieces may be sold as lapidary specimens.
Geological facts
Pink-red coloration usually comes from iron-bearing potassium feldspar, while dark minerals provide contrast. Weathering commonly rounds cobbles and accentuates mineral grains.
Field identification & locations
Look for interlocking visible grains of quartz, feldspar, and dark mica; weak light-dark banding would support gneiss rather than granite. Common in continental shield regions, mountain belts, glacial deposits, and river gravels.
