igneous
Tumbled granite
Granite; chiefly quartz, alkali feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, speckled gray, cream, and black rock with a dull to slightly vitreous luster; hardness about 6–7 Mohs, no cleavage as a whole, and specific gravity roughly 2.63–2.75.
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Physical properties
Coarse-grained, speckled gray, cream, and black rock with a dull to slightly vitreous luster; hardness about 6–7 Mohs, no cleavage as a whole, and specific gravity roughly 2.63–2.75.
Formation & geological history
An intrusive igneous rock crystallized slowly from silica-rich magma deep in Earth’s crust, commonly during Precambrian to Phanerozoic mountain-building events; this specimen has been rounded by tumbling.
Uses & applications
Used extensively for countertops, monuments, building stone, aggregate, and landscaping; polished pebbles are inexpensive decorative and educational specimens.
Geological facts
Visible interlocking grains distinguish granite from fine-grained volcanic rocks such as rhyolite. Black grains are typically biotite or amphibole, while translucent grains are quartz.
Field identification & locations
Identify it by its coarse interlocking texture and three-color speckling; it is common in continental shields, mountain belts, glacial deposits, and river gravels worldwide.
