igneous
Weathered porphyritic granite or granitic gneiss
Quartz–feldspar–mica granitic rock; exact identification requires a fresh surface and mineral tests
AI-generated identification · may be incorrectCoarse, irregular crystalline texture with pale feldspar/quartz and dark biotite or hornblende; likely Mohs 6–7, vitreous to dull luster, no obvious cleavage as a whole, and specific gravity about 2.6–2.8.
Identified More igneous →
Explore Weathered porphyritic granite or granitic gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Coarse, irregular crystalline texture with pale feldspar/quartz and dark biotite or hornblende; likely Mohs 6–7, vitreous to dull luster, no obvious cleavage as a whole, and specific gravity about 2.6–2.8.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep underground, generally during Precambrian to Phanerozoic continental crust formation; surface weathering has produced the brown coating.
Uses & applications
Commonly used as crushed stone, aggregate, building stone, and decorative material; this small weathered fragment has little commercial or collector value.
Geological facts
Granite is identified by visible interlocking quartz and feldspar, commonly with black mica or amphibole. If foliation or banding appears on a fresh break, it may instead be granitic gneiss, a metamorphic equivalent.
Field identification & locations
Look for hard, interlocking grains, pale pink or white feldspar, translucent gray quartz, and black mica; a steel nail will not scratch fresh surfaces, while quartz may scratch glass. Common worldwide in continental shields and mountain belts.
