igneous
Tumbled orbicular granite
Orbicular granite, composed mainly of quartz, feldspar, and mica/amphibole
AI-generated identification · may be incorrectCoarse-grained, black-and-white granite with pink potassium-feldspar patches or orbicules; vitreous to pearly luster, interlocking crystals, and no consistent cleavage as a whole. Hardness is approximately 6–7 Mohs; specific gravity about 2.6–2.8.
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Physical properties
Coarse-grained, black-and-white granite with pink potassium-feldspar patches or orbicules; vitreous to pearly luster, interlocking crystals, and no consistent cleavage as a whole. Hardness is approximately 6–7 Mohs; specific gravity about 2.6–2.8.
Formation & geological history
An intrusive igneous rock crystallized slowly from silica-rich magma, commonly during Precambrian to younger continental plutonic events. The rounded surface indicates human tumbling and polishing.
Uses & applications
Used as a lapidary stone, cabochons, spheres, and decorative aggregate; related granite is widely used for countertops, monuments, and construction.
Geological facts
Its contrasting pink feldspar and dark mafic minerals produce the attractive mottled or orbicular appearance. True orbicular granite contains concentric mineral growths, though this specimen may simply be porphyritic or pegmatitic granite.
Field identification & locations
Identify it by its coarse interlocking crystals, pink feldspar, gray-white quartz/feldspar, and black biotite or hornblende; it is not marble or artificial glass. Common sources include Finland, Madagascar, India, and other granitic regions.
