igneous
Black-and-white granite
Granite, chiefly quartz–alkali feldspar–plagioclase–biotite
AI-generated identification · may be incorrectCoarse-grained, speckled white/gray and black; vitreous quartz, feldspar luster, and dark biotite. Mohs hardness is approximately 6–7; no consistent cleavage as a whole, though feldspar has two cleavages; granular crystalline texture and specific gravity about 2.63–2.75.
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Physical properties
Coarse-grained, speckled white/gray and black; vitreous quartz, feldspar luster, and dark biotite. Mohs hardness is approximately 6–7; no consistent cleavage as a whole, though feldspar has two cleavages; granular crystalline texture and specific gravity about 2.63–2.75.
Formation & geological history
An intrusive felsic igneous rock formed when silica-rich magma cooled slowly deep underground, allowing large crystals to grow. Its exact geological age cannot be determined from the photograph and may range from Precambrian to recent geological periods.
Uses & applications
Widely used as building stone, countertops, monuments, flooring, and aggregate; attractive hand specimens are collected. It is generally low value as a common rock.
Geological facts
The black grains are likely biotite or hornblende, the pale grains feldspar, and any translucent gray grains quartz. The specimen may also be granodiorite if plagioclase dominates, a distinction requiring close examination.
Field identification & locations
Identify it by its interlocking visible crystals and lack of layering or vesicles; granite is common in continental mountain belts and exposed batholiths worldwide. Typical locations include India, Brazil, Canada, the United States, and Scandinavia.
