igneous
Rounded granitic pebble
Granite, likely biotite granite or granodiorite
AI-generated identification · may be incorrectCoarse-grained, speckled gray-brown rock with quartz, feldspar, and dark mica/amphibole; typically Mohs hardness 6–7, vitreous-to-earthy luster, interlocking crystals, and no cleavage as a whole rock. Its rounded shape indicates abrasion and weathering.
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Physical properties
Coarse-grained, speckled gray-brown rock with quartz, feldspar, and dark mica/amphibole; typically Mohs hardness 6–7, vitreous-to-earthy luster, interlocking crystals, and no cleavage as a whole rock. Its rounded shape indicates abrasion and weathering.
Formation & geological history
Formed when silica-rich magma slowly crystallized deep underground, generally in Precambrian to Phanerozoic continental crust; later exposed and rounded by river, beach, or glacial transport.
Uses & applications
Common granite is used as crushed aggregate, dimension stone, paving, countertops, and landscaping material; an ordinary pebble has little jewelry value.
Geological facts
The pale grains are usually quartz and feldspar, while black grains are biotite or hornblende. Exact identification requires a fresh surface, hand lens, and sometimes thin-section or chemical analysis.
Field identification & locations
Identify it by visible interlocking light and dark crystals, lack of layering or foliation, and inability to scratch individual quartz grains with a steel knife. Common worldwide in granitic terrains and stream gravels.
