igneous
Granite
Coarse-grained felsic intrusive igneous rock, typically quartz + alkali feldspar + plagioclase + biotite/hornblende
AI-generated identification · may be incorrectHardness about 6–7; light gray to pinkish-white with black mafic flecks, granular texture, and generally vitreous-to-dull luster. Interlocking crystals are visible; cleavage belongs to individual feldspar minerals, not the rock as a whole; specific gravity is approximately 2.63–2.75.
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Physical properties
Hardness about 6–7; light gray to pinkish-white with black mafic flecks, granular texture, and generally vitreous-to-dull luster. Interlocking crystals are visible; cleavage belongs to individual feldspar minerals, not the rock as a whole; specific gravity is approximately 2.63–2.75.
Formation & geological history
Formed when silica-rich magma cooled slowly deep underground, producing large crystals; most granite bodies formed during Precambrian to Phanerozoic plutonic events. The rounded shape and surface wear indicate natural weathering or handling.
Uses & applications
Widely used as dimension stone, countertops, monuments, paving, aggregate, and building stone; attractive polished pieces are also collected. This specimen is likely worth about $5–$20 unless unusually patterned, locality-documented, or unusually large.
Geological facts
The black grains are commonly biotite mica or hornblende, while the pale grains are feldspar and quartz. Granite is the intrusive equivalent of rhyolite and commonly forms continental mountain roots.
Field identification & locations
Identify it by its coarse interlocking crystals, light color, and abundant quartz/feldspar with scattered dark minerals; it should not fizz with dilute hydrochloric acid. Common worldwide, especially in continental shields and mountain belts.
