igneous
Porphyritic granite (likely orbicular/porphyritic granitoid)
Quartz–feldspar granitoid; commonly composed of K-feldspar, plagioclase, quartz, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, light gray to pinkish rock with conspicuous rounded or blocky feldspar crystals in a finer crystalline matrix; generally Mohs 6–7, vitreous quartz luster, no cleavage as a rock, and specific gravity about 2.6–2.7.
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Physical properties
Coarse-grained, light gray to pinkish rock with conspicuous rounded or blocky feldspar crystals in a finer crystalline matrix; generally Mohs 6–7, vitreous quartz luster, no cleavage as a rock, and specific gravity about 2.6–2.7.
Formation & geological history
Intrusive igneous rock formed by slow crystallization of silica-rich magma deep in the crust, probably during a Precambrian to Phanerozoic plutonic event; the exact age cannot be determined from the image.
Uses & applications
Used as dimension stone, countertops, monuments, aggregate, and landscaping rock; attractive specimens may be collected for their large feldspar phenocrysts.
Geological facts
The prominent crystals indicate porphyritic texture, reflecting two-stage cooling: early feldspar growth followed by slower crystallization of the surrounding magma.
Field identification & locations
Identify by its interlocking crystals, hardness, lack of bedding, and inability to scratch with a steel knife; a streakless, glassy quartz component and abundant feldspar distinguish it from many sedimentary rocks. Common in continental plutons worldwide.
