igneous
Weathered granite or granitic gneiss fragment
Quartz–feldspar–mica granite; possibly foliated granitic gneiss
AI-generated identification · may be incorrectCoarse, mottled white-gray and dark mineral grains indicate quartz, feldspar, and biotite/hornblende; likely Mohs hardness 6–7, vitreous to dull luster, interlocking crystalline texture, and no obvious cleavage as a whole rock.
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Physical properties
Coarse, mottled white-gray and dark mineral grains indicate quartz, feldspar, and biotite/hornblende; likely Mohs hardness 6–7, vitreous to dull luster, interlocking crystalline texture, and no obvious cleavage as a whole rock.
Formation & geological history
Granite crystallizes slowly from silica-rich magma deep underground, commonly during Precambrian to Phanerozoic continental mountain-building; gneissic varieties are later recrystallized and deformed by high-grade metamorphism.
Uses & applications
Common granite is widely used as crushed aggregate, dimension stone, countertops, monuments, and building cladding; attractive polished pieces may be collected but usually have modest value.
Geological facts
The pale minerals are probably feldspar and quartz, while dark flecks are mica or amphibole. The irregular rusty-brown surface likely reflects weathering of iron-bearing minerals.
Field identification & locations
Identify it by visible interlocking light and dark crystals, unlike sedimentary rocks with layers or fossils; a streak test is usually white, and it should not fizz strongly in dilute acid. Common worldwide in continental crust and glacial or stream gravels.
