igneous
Rounded granite cobble
Granite, a coarse-grained felsic intrusive igneous rock composed mainly of quartz, potassium feldspar, plagioclase, and minor mica or amphibole
AI-generated identification · may be incorrectGray, speckled, and weakly granular with a dull to slightly vitreous luster; individual crystals are visible but softened by weathering or polishing. Hardness is approximately 6–7 Mohs; no strong cleavage as a whole, though feldspar and mica grains cleave; specific gravity is about 2.63–2.75.
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Physical properties
Gray, speckled, and weakly granular with a dull to slightly vitreous luster; individual crystals are visible but softened by weathering or polishing. Hardness is approximately 6–7 Mohs; no strong cleavage as a whole, though feldspar and mica grains cleave; specific gravity is about 2.63–2.75.
Formation & geological history
Formed when silica-rich magma cooled slowly deep within the continental crust, allowing large interlocking crystals to grow; most granite formed during Precambrian to Phanerozoic geologic periods. Its rounded shape indicates transport and abrasion by a stream, beach, or glacial environment.
Uses & applications
Used as dimension stone, countertops, monuments, paving, aggregate, and landscaping material; attractive polished pieces are collected as representative igneous specimens. This common cobble has little commercial value.
Geological facts
The light-gray color and scattered dark grains are typical of granite, but image resolution makes exact identification uncertain; granodiorite or weathered gneiss are possible alternatives.
Field identification & locations
Identify it by interlocking light quartz/feldspar grains, darker mica or amphibole flecks, granular texture, and lack of layering or vesicles. Common worldwide, especially in regions exposing continental plutons.
