igneous
Granite or granitic gneiss
Granite; chiefly quartz, feldspar, and mica
AI-generated identification · may be incorrectCoarse-grained, speckled gray rock with white/pink feldspar, translucent quartz, and dark biotite or amphibole; typically Mohs 6–7, vitreous to dull luster, with no prominent cleavage as a whole. The texture appears granular and massive, though weathering obscures details.
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Physical properties
Coarse-grained, speckled gray rock with white/pink feldspar, translucent quartz, and dark biotite or amphibole; typically Mohs 6–7, vitreous to dull luster, with no prominent cleavage as a whole. The texture appears granular and massive, though weathering obscures details.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in the continental crust, generally during Precambrian to Phanerozoic mountain-building events; if foliated, it may instead be granitic gneiss formed by high-grade metamorphism.
Uses & applications
Widely used as crushed aggregate, road material, dimension stone, countertops, monuments, and building facades; ordinary loose specimens have little jewelry value.
Geological facts
Granite’s interlocking crystals make it durable and resistant to abrasion. Pink coloration commonly reflects potassium feldspar, while dark grains are usually biotite or amphibole.
Field identification & locations
Identify it by visible interlocking crystals and a salt-and-pepper appearance; a streak test is generally unhelpful. Common worldwide in continental shields, batholiths, quarries, and glacial deposits; distinguishing granite from gneiss requires checking for mineral banding or foliation.
