igneous
Porphyritic granite (weathered granitic rock)
Granite, likely biotite–hornblende porphyritic granite
AI-generated identification · may be incorrectCoarse-grained, tan to pink matrix with visible dark biotite/hornblende and reddish feldspar crystals; quartz is likely present. Hardness is roughly 6–7 Mohs, with vitreous quartz, feldspar cleavage, and typical specific gravity of 2.6–2.8.
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Physical properties
Coarse-grained, tan to pink matrix with visible dark biotite/hornblende and reddish feldspar crystals; quartz is likely present. Hardness is roughly 6–7 Mohs, with vitreous quartz, feldspar cleavage, and typical specific gravity of 2.6–2.8.
Formation & geological history
An intrusive igneous rock formed when silica-rich magma cooled slowly deep within the continental crust, allowing large crystals to grow; commonly Precambrian to Phanerozoic in age. Surface weathering has rounded and stained the specimen.
Uses & applications
Widely used as dimension stone, countertops, paving, monuments, aggregate, and crushed stone; attractive pieces may be collected or polished.
Geological facts
The large contrasting crystals give it a porphyritic texture, recording cooling in more than one stage. Dark minerals are commonly biotite mica and/or hornblende, while pink grains are potassium feldspar.
Field identification & locations
Identify it by its interlocking visible crystals, abundant light quartz/feldspar, and scattered black mica or amphibole; it should not fizz with dilute hydrochloric acid. Common worldwide in continental plutons, including India, Canada, Brazil, and the United States.
