igneous
Orbicular granite (likely Rapakivi-type granite)
Granite, chiefly quartz, alkali feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, mottled black, gray, and cream rock with interlocking crystals; quartz and feldspar are Mohs 6–7, with vitreous to pearly luster. The image appears polished, so exact grain boundaries and texture are partly obscured.
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Physical properties
Coarse-grained, mottled black, gray, and cream rock with interlocking crystals; quartz and feldspar are Mohs 6–7, with vitreous to pearly luster. The image appears polished, so exact grain boundaries and texture are partly obscured.
Formation & geological history
A plutonic igneous rock crystallized slowly from silica-rich magma deep in the crust, typically during Precambrian to Phanerozoic intrusive events. Orbicular varieties develop rounded feldspar-rich structures during unusual magma crystallization or metasomatic processes.
Uses & applications
Used for countertops, tiles, monuments, facing stone, and decorative polished slabs; attractive orbicular material is also collected. Common granite has substantial construction value, while rare orbicular varieties command higher prices.
Geological facts
Its light minerals are feldspar and quartz, while dark minerals are usually biotite or amphibole. Orbicular patterns can resemble leopard skin but are geological, not fossil or organic.
Field identification & locations
Identify it by coarse interlocking crystals, lack of layering, hardness, and resistance to scratching; a streak test is usually white to pale gray. Common sources include Finland, Sweden, Madagascar, India, Brazil, and numerous granite provinces worldwide.
