igneous
Granite (biotite-bearing, possibly pegmatitic granite)
Felsic intrusive igneous rock; chiefly quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectMedium- to coarse-grained, white to pale gray with black flaky biotite or hornblende; vitreous quartz and pearly mica luster, interlocking crystals, no cleavage as a whole. Individual minerals are roughly Mohs 2–7; specific gravity about 2.6–2.7.
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Physical properties
Medium- to coarse-grained, white to pale gray with black flaky biotite or hornblende; vitreous quartz and pearly mica luster, interlocking crystals, no cleavage as a whole. Individual minerals are roughly Mohs 2–7; specific gravity about 2.6–2.7.
Formation & geological history
Slow cooling of silica-rich magma deep in the continental crust, allowing large crystals to form; commonly Precambrian to Phanerozoic in age.
Uses & applications
Widely used as dimension stone, countertops, monuments, aggregate, and decorative material; attractive hand specimens have modest collecting value.
Geological facts
The black minerals are likely biotite and/or hornblende, while translucent grains are quartz and white grains are feldspar. Its granular texture distinguishes it from volcanic rhyolite.
Field identification & locations
Common in continental mountain belts and exposed batholiths worldwide; identify by its interlocking white, gray, glassy, and black mineral grains. A streak test is generally unhelpful, but a steel knife may scratch feldspar more readily than quartz.
