igneous
Granite
Granite; primarily quartz, potassium feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectLight gray, coarse-grained, speckled black-and-white, with a granular texture and mostly vitreous-to-dull luster. Typical Mohs hardness is 6–7; crystals are interlocking and lack prominent cleavage as a whole, though feldspar grains cleave.
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Physical properties
Light gray, coarse-grained, speckled black-and-white, with a granular texture and mostly vitreous-to-dull luster. Typical Mohs hardness is 6–7; crystals are interlocking and lack prominent cleavage as a whole, though feldspar grains cleave.
Formation & geological history
Granite forms when silica-rich magma cools slowly deep within continental crust, allowing large crystals to grow; individual specimens may range from Precambrian to recent geologic ages. It is commonly exposed by uplift and erosion of plutonic bodies.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving, aggregate, and building stone; attractive polished pieces are also collected. This small fragment has little commercial value.
Geological facts
The black grains are likely biotite or hornblende, while the pale grains are feldspar and quartz. Its coarse texture distinguishes it from fine-grained volcanic rocks such as rhyolite.
Field identification & locations
Identify it by visible interlocking crystals, light overall color, and black mineral flecks; a glassy quartz grain will not scratch easily, while feldspar commonly shows cleavage. Common localities include continental mountain belts worldwide, including India, Brazil, Scandinavia, and the United States.
