igneous
Granite pebble
Granite, a felsic intrusive igneous rock composed chiefly of quartz, potassium feldspar, and plagioclase, with minor biotite or amphibole
AI-generated identification · may be incorrectCoarse, visibly speckled texture; pinkish-brown, gray, white, and dark mineral grains; vitreous quartz and feldspar luster; Mohs hardness about 6–7; generally massive with no cleavage as a whole, though feldspar grains cleave. Specific gravity is typically 2.63–2.75.
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Physical properties
Coarse, visibly speckled texture; pinkish-brown, gray, white, and dark mineral grains; vitreous quartz and feldspar luster; Mohs hardness about 6–7; generally massive with no cleavage as a whole, though feldspar grains cleave. Specific gravity is typically 2.63–2.75.
Formation & geological history
Formed when silica-rich magma slowly cooled and crystallized deep in Earth’s crust, commonly during Precambrian to Mesozoic plutonic events; the rounded shape indicates later weathering and transport.
Uses & applications
Widely used for countertops, monuments, building stone, aggregate, and landscaping; small pieces are mainly sold as inexpensive educational or decorative specimens.
Geological facts
The interlocking crystals indicate slow underground cooling, unlike volcanic rhyolite, which is often fine-grained. Pink coloration commonly comes from potassium feldspar.
Field identification & locations
Identify it by its coarse interlocking grains, quartz’s glassy gray appearance, pink/white feldspar, and scattered black mica or amphibole. Common worldwide in continental crust and stream or glacial gravels.
