igneous
Rounded granite or granitic gneiss cobble
Granite, chiefly quartz, potassium feldspar, plagioclase, and biotite/hornblende
AI-generated identification · may be incorrectCoarse speckled texture with pale feldspar/quartz and dark mica or amphibole; typically Mohs 6–7, nonmetallic and dull to slightly vitreous, with interlocking crystals and no cleavage as a whole rock. The smooth shape is from water or glacial abrasion.
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Physical properties
Coarse speckled texture with pale feldspar/quartz and dark mica or amphibole; typically Mohs 6–7, nonmetallic and dull to slightly vitreous, with interlocking crystals and no cleavage as a whole rock. The smooth shape is from water or glacial abrasion.
Formation & geological history
Crystallized slowly from silica-rich magma deep in the crust, commonly during Precambrian to Mesozoic mountain-building; later exposed and rounded by erosion. If faint banding is present, it may instead be granitic gneiss, a metamorphosed equivalent.
Uses & applications
Used as aggregate, building stone, paving, monuments, countertops, and landscaping rock; rounded examples are mainly decorative or educational specimens.
Geological facts
Granite’s visible crystals indicate slow underground cooling. Individual mineral grains can often be scratched only by harder materials such as quartz or steel.
Field identification & locations
Common in continental shields, mountain belts, streambeds, glacial deposits, and coastal beaches. Identify it by its light background, black mineral flecks, interlocking crystalline texture, and lack of layers or vesicles.
