igneous
Biotite granite pebble
Granite, chiefly quartz (SiO₂), feldspar, and biotite mica
AI-generated identification · may be incorrectCoarse-grained, speckled cream-white and black; likely Mohs 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole. The black flakes are probably biotite, while the pale crystals are feldspar and quartz.
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Physical properties
Coarse-grained, speckled cream-white and black; likely Mohs 6–7, vitreous to dull luster, interlocking crystals, and no prominent cleavage as a whole. The black flakes are probably biotite, while the pale crystals are feldspar and quartz.
Formation & geological history
An intrusive igneous rock that crystallized slowly from silica-rich magma deep underground, commonly during Precambrian to Phanerozoic mountain-building events. Its rounded shape indicates later erosion and transport as a pebble.
Uses & applications
Used widely as dimension stone, countertops, monuments, crushed aggregate, and building material; ordinary pebbles have little commercial value.
Geological facts
Granite’s visible crystals record slow cooling beneath Earth’s surface. Weathering commonly alters feldspar to cream or tan tones and can produce rusty iron-oxide staining.
Field identification & locations
Common in continental crust and found in granite terrains worldwide, including North America, Europe, and India. Identify it by its coarse interlocking quartz–feldspar–mica texture; a hand lens helps distinguish mica flakes from dark amphibole.
