igneous
Black-and-white granite
Granite, typically quartz–feldspar–biotite granite
AI-generated identification · may be incorrectCoarse-grained, speckled white, gray, and black; interlocking crystals with glassy quartz and pearly feldspar. Hardness is approximately 6–7 Mohs; no dominant cleavage as a whole rock; specific gravity about 2.6–2.7; generally nonmetallic luster.
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Physical properties
Coarse-grained, speckled white, gray, and black; interlocking crystals with glassy quartz and pearly feldspar. Hardness is approximately 6–7 Mohs; no dominant cleavage as a whole rock; specific gravity about 2.6–2.7; generally nonmetallic luster.
Formation & geological history
An intrusive felsic igneous rock formed when silica-rich magma cooled slowly deep underground, allowing large crystals to grow. Individual pieces may range from Precambrian to much younger Phanerozoic ages, depending on locality.
Uses & applications
Widely used as building stone, countertops, monuments, flooring, aggregate, and polished decorative material. Ordinary hand specimens usually have modest collector value.
Geological facts
The black minerals are commonly biotite mica and/or hornblende, while white areas are mainly feldspar and translucent gray grains are quartz. Its coarse texture distinguishes it from fine-grained volcanic rhyolite.
Field identification & locations
Identify it by visible interlocking quartz, feldspar, and dark mica/hornblende crystals, lack of layering, and a very hard texture; a steel blade generally does not scratch quartz. Common worldwide in continental batholiths and mountain belts.
