igneous
Granite
Granite; chiefly quartz, plagioclase and alkali feldspar, with biotite or hornblende
AI-generated identification · may be incorrectCoarse-grained, speckled gray-and-white rock with glassy quartz and pale feldspar; Mohs hardness about 6–7, granular crystal structure, no cleavage as a whole, and specific gravity about 2.63–2.75. The dark grains are likely biotite or amphibole.
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Physical properties
Coarse-grained, speckled gray-and-white rock with glassy quartz and pale feldspar; Mohs hardness about 6–7, granular crystal structure, no cleavage as a whole, and specific gravity about 2.63–2.75. The dark grains are likely biotite or amphibole.
Formation & geological history
An intrusive igneous rock formed by slow crystallization of silica-rich magma deep within Earth’s crust, commonly during Precambrian through Phanerozoic mountain-building events. Exact age cannot be determined from the photograph.
Uses & applications
Used extensively as building stone, countertops, monuments, paving, crushed aggregate, and decorative material; attractive polished pieces are also collected.
Geological facts
Its visible interlocking crystals indicate slow underground cooling, unlike volcanic rocks such as rhyolite. Color and grain size vary with feldspar, quartz, and dark-mineral proportions.
Field identification & locations
Identify it by its coarse interlocking grains, abundant light feldspar/quartz, and scattered dark mica or amphibole; it does not fizz with dilute hydrochloric acid. Common worldwide in continental mountain belts and exposed batholiths.
