igneous
Porphyritic granite or granitic gneiss
Quartz–feldspar–mica granitoid; exact identification requires testing
AI-generated identification · may be incorrectCoarse, irregular interlocking crystals with pale feldspar, translucent-gray quartz, and dark mica/amphibole; likely Mohs 6–7, vitreous to dull luster, with poor cleavage as a whole and mineral-specific cleavage. The rounded shape appears naturally weathered or water-worn.
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Physical properties
Coarse, irregular interlocking crystals with pale feldspar, translucent-gray quartz, and dark mica/amphibole; likely Mohs 6–7, vitreous to dull luster, with poor cleavage as a whole and mineral-specific cleavage. The rounded shape appears naturally weathered or water-worn.
Formation & geological history
Likely crystallized slowly from silica-rich magma deep in continental crust, generally Precambrian to Mesozoic depending on locality; surface exposure and weathering produced the rounded specimen.
Uses & applications
Common granite is used for construction aggregate, monuments, countertops, and dimension stone; attractive pieces may be collected, but this small specimen has little commercial value.
Geological facts
The visible large crystals indicate slow cooling, while gray-dark patches may reflect biotite or amphibole and weathering. A streak test should be white, and the rock should not fizz with dilute hydrochloric acid.
Field identification & locations
Common in continental shields, mountain belts, and stream gravels worldwide. Confirm with a steel scratch test, glass scratch test, hand lens, and examination of thin-section mineral textures; the photo alone cannot distinguish granite from gneiss confidently.
