igneous
Biotite-bearing granite
Granite, chiefly quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, light gray to cream rock with glassy quartz, white feldspar, and black platy biotite; Mohs hardness about 6–7, nonfoliated, with feldspar cleavage and quartz lacking cleavage. Luster is vitreous on quartz and pearly on mica; typical specific gravity is 2.6–2.7.
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Physical properties
Coarse-grained, light gray to cream rock with glassy quartz, white feldspar, and black platy biotite; Mohs hardness about 6–7, nonfoliated, with feldspar cleavage and quartz lacking cleavage. Luster is vitreous on quartz and pearly on mica; typical specific gravity is 2.6–2.7.
Formation & geological history
Slow cooling of silica-rich magma deep in the continental crust produced interlocking crystals, commonly during Precambrian to Mesozoic plutonic events. Weathering has slightly stained the surface brown.
Uses & applications
Widely used as building stone, countertops, monuments, flooring aggregate, and crushed stone; attractive specimens are collected but usually have modest value.
Geological facts
The black flakes are biotite, whose reflective cleavage surfaces can sparkle when rotated. Granite is one of Earth’s most abundant continental crust rocks.
Field identification & locations
Identify it by its visible quartz, feldspar, and black mica grains, lack of layering, and granular texture; it is common in continental mountain belts and exposed plutons worldwide, including India, Canada, Brazil, and the United States.
