igneous
Porphyritic granite
Biotite–feldspar granite, likely weathered
AI-generated identification · may be incorrectCoarse-grained, speckled rock with pale quartz/feldspar, darker biotite or hornblende, and possible bluish-gray feldspar; nonmetallic luster, irregular fracture, Mohs hardness about 6–7, no obvious cleavage as a whole. The brown surface reflects weathering or iron staining.
Identified More igneous →
Explore Porphyritic granite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse-grained, speckled rock with pale quartz/feldspar, darker biotite or hornblende, and possible bluish-gray feldspar; nonmetallic luster, irregular fracture, Mohs hardness about 6–7, no obvious cleavage as a whole. The brown surface reflects weathering or iron staining.
Formation & geological history
Intrusive igneous rock formed when silica-rich magma cooled slowly several kilometers underground, producing interlocking crystals; generally Precambrian to Mesozoic depending on locality. Subsequent exposure weathered the outer surface.
Uses & applications
Used widely as crushed aggregate, building stone, paving, countertops, monuments, and decorative landscaping material; this small weathered fragment has little gem or collector value.
Geological facts
Granite is defined by abundant quartz and alkali feldspar and commonly contains plagioclase, mica, and amphibole. Its interlocking texture makes it durable and resistant to abrasion.
Field identification & locations
Identify it by visible interlocking crystals, pale quartz/feldspar, and scattered dark minerals; a glassy surface, acid test, and hand lens help distinguish it from concrete. Common worldwide in continental shields, batholiths, and mountain belts.
