igneous
Biotite granite (possibly granodiorite)
Coarse-grained granitoid composed mainly of quartz (SiO₂), potassium feldspar, plagioclase, biotite, and minor amphibole
AI-generated identification · may be incorrectHardness about 6–7; speckled white, gray, black, and olive-brown appearance; vitreous quartz and pearly-to-submetallic mica; interlocking phaneritic crystals with no prominent cleavage as a whole, though feldspar and biotite cleave. Typical specific gravity is 2.6–2.8.
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Physical properties
Hardness about 6–7; speckled white, gray, black, and olive-brown appearance; vitreous quartz and pearly-to-submetallic mica; interlocking phaneritic crystals with no prominent cleavage as a whole, though feldspar and biotite cleave. Typical specific gravity is 2.6–2.8.
Formation & geological history
Slow crystallization of silica-rich magma deep in the crust produced the coarse texture, generally during Precambrian to Phanerozoic continental plutonism. Rounded edges indicate later weathering or tumbling.
Uses & applications
Used for countertops, building stone, monuments, paving, and aggregate; attractive polished pieces are collected as geological specimens. It is generally not a gemstone.
Geological facts
The dark flakes are likely biotite and/or amphibole, while translucent gray grains are quartz and pale grains are feldspar. Granite is a major component of continental crust.
Field identification & locations
Identify it by visible interlocking crystals, abundant pale feldspar/quartz, and dark mica or amphibole; it is commonly found in continental mountain belts and glacial deposits. A thin section or hardness and acid tests can distinguish granite from granodiorite.
