igneous
Biotite-rich granite or granitic gneiss
Quartz–feldspar–biotite rock; likely granite, possibly weakly foliated gneiss
AI-generated identification · may be incorrectCoarse-grained, brown-gray specimen with visible translucent quartz, pale feldspar, and dark mica; vitreous-to-earthy luster, interlocking crystals, no obvious cleavage as a whole, Mohs hardness about 6–7, specific gravity roughly 2.6–2.8.
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Physical properties
Coarse-grained, brown-gray specimen with visible translucent quartz, pale feldspar, and dark mica; vitreous-to-earthy luster, interlocking crystals, no obvious cleavage as a whole, Mohs hardness about 6–7, specific gravity roughly 2.6–2.8.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep underground, commonly during Precambrian to Phanerozoic continental mountain-building; gneissic texture forms if later subjected to high-grade metamorphism.
Uses & applications
Used as crushed aggregate, building stone, monuments, countertops, and landscaping rock; attractive polished pieces have modest collecting value.
Geological facts
The rounded shape and surface wear indicate transport as a cobble or deliberate polishing, while the granular texture distinguishes it from basalt and glass.
Field identification & locations
Identify it by its coarse interlocking quartz-feldspar-mica grains, lack of vesicles, and light-to-dark speckled appearance; common worldwide, especially in continental shields and mountain belts.
