igneous
Orbicular granite (likely rapakivi-type granite)
Granite; chiefly quartz, alkali feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, tan-pink rock with black mafic minerals and rounded feldspar-rich orbicules; interlocking crystalline texture, vitreous-to-dull luster, Mohs hardness about 6–7, no prominent cleavage as a rock, specific gravity roughly 2.6–2.8.
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Physical properties
Coarse-grained, tan-pink rock with black mafic minerals and rounded feldspar-rich orbicules; interlocking crystalline texture, vitreous-to-dull luster, Mohs hardness about 6–7, no prominent cleavage as a rock, specific gravity roughly 2.6–2.8.
Formation & geological history
Slow cooling of silica-rich magma deep in the crust produced the granite; orbicular textures formed through unusual crystal nucleation and mineral-rich fluids. Such granites are generally Precambrian to younger, depending on locality.
Uses & applications
Used as decorative facing stone, countertops, tiles, monuments, and polished lapidary pieces; attractive hand specimens are collected.
Geological facts
The rounded patterns are natural orbicules, not fossil structures. Black patches commonly represent biotite or hornblende concentrated around feldspar growths.
Field identification & locations
Identify it by its coarse interlocking crystals, abundant pale feldspar, quartz, and scattered black mica/amphibole; a fresh surface should not resemble uniform concrete. Orbicular granites are notably associated with Finland, Madagascar, Corsica, and parts of North America.
