igneous
Weathered granite or granitic gneiss
Quartz–feldspar–mica granitoid; possible biotite granite or gneiss
AI-generated identification · may be incorrectCoarse, irregular interlocking grains with pale gray quartz/feldspar and dark brown-black biotite or iron-oxide staining; likely Mohs 6–7, vitreous to dull luster, poor cleavage as a whole, and specific gravity about 2.6–2.8.
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Physical properties
Coarse, irregular interlocking grains with pale gray quartz/feldspar and dark brown-black biotite or iron-oxide staining; likely Mohs 6–7, vitreous to dull luster, poor cleavage as a whole, and specific gravity about 2.6–2.8.
Formation & geological history
Formed by slow crystallization of silica-rich magma deep in the crust; if gneissic, it was later subjected to high-grade metamorphism. The specimen’s exact age and classification cannot be determined reliably from the photograph.
Uses & applications
Commonly used as crushed aggregate, dimension stone, building stone, and landscape material; attractive polished pieces may be used decoratively.
Geological facts
Granite is identified by visible quartz and feldspar crystals, while gneiss commonly shows compositional banding; this fragment appears strongly weathered and lacks clear banding.
Field identification & locations
Look for hard, glassy gray quartz, blocky white or pink feldspar, and dark mica flakes; a knife will not scratch fresh surfaces, but quartz can scratch glass. Common worldwide in continental crust and exposed mountain belts.
