igneous
Biotite-bearing granite or granitic gneiss
Quartz–feldspar–biotite granite; possibly weakly foliated granitic gneiss
AI-generated identification · may be incorrectCoarse-grained, mottled white/gray/pink specimen with translucent quartz, pale feldspar, and black platy biotite or amphibole. Hardness about 6–7 Mohs; vitreous quartz luster, feldspar cleavage, and massive to weakly foliated texture; specific gravity roughly 2.6–2.8.
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Physical properties
Coarse-grained, mottled white/gray/pink specimen with translucent quartz, pale feldspar, and black platy biotite or amphibole. Hardness about 6–7 Mohs; vitreous quartz luster, feldspar cleavage, and massive to weakly foliated texture; specific gravity roughly 2.6–2.8.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep in the crust, generally during Precambrian to Phanerozoic plutonic events; gneissic texture indicates later high-grade metamorphism. Common in continental crust, mountain belts, and exposed basement terrains.
Uses & applications
Used as dimension stone, countertops, monuments, aggregate, and architectural facing; attractive polished pieces may be collected but are usually low-value.
Geological facts
Quartz appears glassy and gray, feldspar is cloudy white or pink, and dark mica commonly forms black flakes. Alternating mineral-rich bands would support identification as granitic gneiss rather than ordinary granite.
Field identification & locations
Identify by its visible interlocking crystals and lack of vesicles or sedimentary layering; a streak test, hand lens, and hardness test help distinguish it from softer look-alikes. Common worldwide, especially in continental shield and mountain regions.
