igneous
Weathered granite or granitic gneiss cobble
Granite, chiefly quartz, feldspar, and dark mica/amphibole
AI-generated identification · may be incorrectCoarse, speckled texture with pale feldspar/quartz and black mafic minerals; brown-red coloration is likely iron-oxide weathering. Hardness about 6–7 Mohs, nonmetallic luster, granular interlocking crystals, and no obvious cleavage as a whole rock.
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Physical properties
Coarse, speckled texture with pale feldspar/quartz and black mafic minerals; brown-red coloration is likely iron-oxide weathering. Hardness about 6–7 Mohs, nonmetallic luster, granular interlocking crystals, and no obvious cleavage as a whole rock.
Formation & geological history
Formed by slow crystallization of silica-rich magma deep in Earth, commonly during Precambrian to Phanerozoic continental crust formation; later uplift, weathering, and stream or glacial transport rounded the cobble.
Uses & applications
Crushed granite is widely used as aggregate, road stone, building stone, and monuments; attractive polished pieces are used decoratively but this specimen has limited gem value.
Geological facts
The rounded shape and iron-stained surface indicate prolonged weathering and abrasion. Dark seams may represent biotite-rich layers, amphibole, or minor quartz veins.
Field identification & locations
Identify it by visible interlocking quartz and feldspar grains, scattered black minerals, high hardness, and lack of layering; common in continental mountain belts, glacial deposits, and river gravels.
