igneous
Porphyritic granite
Porphyritic granitoid, composed mainly of quartz and feldspar with dark mica or amphibole
AI-generated identification · may be incorrectCoarse-grained, light-colored rock with conspicuous larger crystals in a finer crystalline groundmass; likely Mohs hardness 6–7, vitreous quartz and feldspar luster, with no consistent cleavage as a whole. The image’s pale, weathered surface makes exact mineral identification uncertain.
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Physical properties
Coarse-grained, light-colored rock with conspicuous larger crystals in a finer crystalline groundmass; likely Mohs hardness 6–7, vitreous quartz and feldspar luster, with no consistent cleavage as a whole. The image’s pale, weathered surface makes exact mineral identification uncertain.
Formation & geological history
Formed when silica-rich magma cooled slowly underground, allowing large crystals to grow before the remaining melt solidified; typically Precambrian to Phanerozoic, depending on the intrusion.
Uses & applications
Used as dimension stone, building and paving material, countertops, monuments, and decorative aggregate.
Geological facts
The contrasting large crystals are called phenocrysts; their size difference records changing cooling conditions during crystallization.
Field identification & locations
Look for interlocking quartz and feldspar crystals, with scattered larger grains and occasional dark minerals. Granitoids are widespread in continental crust worldwide; a fresh broken surface is more diagnostic than a weathered one.
