igneous
Polished/rounded granite cobble
Granite, chiefly quartz (SiO₂), feldspar, and mica/amphibole
AI-generated identification · may be incorrectCoarse-grained, speckled white, gray, black, and pink mineral pattern; interlocking crystals, generally vitreous to dull luster, no obvious cleavage as a whole, Mohs hardness about 6–7, specific gravity 2.63–2.75.
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Physical properties
Coarse-grained, speckled white, gray, black, and pink mineral pattern; interlocking crystals, generally vitreous to dull luster, no obvious cleavage as a whole, Mohs hardness about 6–7, specific gravity 2.63–2.75.
Formation & geological history
An intrusive igneous rock crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic mountain-building events. Its rounded shape and smooth surface result from transport and abrasion, likely in a river, beach, or glacial deposit.
Uses & applications
Used extensively as dimension stone, countertops, monuments, paving, aggregate, landscaping stone, and decorative specimens; this rounded piece has modest collector value.
Geological facts
The contrasting pattern reflects large interlocking crystals formed during slow cooling. Pink areas are commonly potassium feldspar, white areas plagioclase or quartz, and dark grains biotite, hornblende, or other mafic minerals.
Field identification & locations
Identify granite by its visible interlocking crystals and mixed quartz–feldspar–dark-mineral coloration; it is not layered and does not react strongly with dilute acid. Common worldwide, especially in exposed continental shield and mountain regions.
