igneous
Tumbled granite pebble
Granite, primarily quartz–feldspar–mica aggregate
AI-generated identification · may be incorrectHardness about 6–7 Mohs; rounded and polished, with pink/tan feldspar, gray quartz, and dark biotite or hornblende. Coarse crystalline texture, generally non-cleaved, and vitreous to dull luster; density about 2.6–2.7 g/cm³.
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Physical properties
Hardness about 6–7 Mohs; rounded and polished, with pink/tan feldspar, gray quartz, and dark biotite or hornblende. Coarse crystalline texture, generally non-cleaved, and vitreous to dull luster; density about 2.6–2.7 g/cm³.
Formation & geological history
Intrusive igneous rock formed when silica-rich magma slowly crystallized deep in Earth’s crust, commonly during Precambrian to Phanerozoic mountain-building events. The shape shown is produced by natural abrasion or tumbling.
Uses & applications
Used widely as crushed aggregate, building stone, countertops, monuments, and landscaping material; small polished pieces are sold as decorative specimens or craft stones.
Geological facts
Granite’s visible grains indicate slow cooling, unlike volcanic rocks that cool at the surface. Pink coloration usually reflects potassium feldspar, while black grains commonly represent biotite or amphibole.
Field identification & locations
Identify it by its interlocking coarse grains and mixed pink, gray, white, and black colors; it will not fizz with dilute hydrochloric acid. Common worldwide, especially in continental shields and mountain belts; confirm with a hardness test and close inspection.
