igneous
Rounded granite cobble
Granite, a coarse-grained felsic intrusive igneous rock composed mainly of quartz, feldspar, and mica
AI-generated identification · may be incorrectGray, speckled, granular surface with a small tan mineral stain; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no cleavage as a whole rock. The oval shape and smooth surface indicate prolonged abrasion or weathering.
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Physical properties
Gray, speckled, granular surface with a small tan mineral stain; typically Mohs 6–7, vitreous to dull luster, interlocking crystals, and no cleavage as a whole rock. The oval shape and smooth surface indicate prolonged abrasion or weathering.
Formation & geological history
Granite forms when silica-rich magma cools slowly underground, commonly producing crystals millions to billions of years ago. The rounded cobble was likely shaped later by river transport, waves, or glacial action.
Uses & applications
Granite is widely used for building stone, paving, countertops, and monuments; this cobble is chiefly decorative or suitable for collecting.
Geological facts
Its visible grains are interlocking crystals, rather than sediment cemented together; individual mineral grains may include quartz, feldspar, and dark mica or amphibole.
Field identification & locations
Identify it by the salt-and-pepper texture and hard, interlocking grains; quartz typically scratches glass. Granite is widespread in continental crust, and rounded cobbles commonly occur in riverbeds, beaches, and glacial deposits.
