igneous
Weathered granitic pebble
Granite or granodiorite; chiefly quartz, feldspar, and mica, with iron-oxide staining
AI-generated identification · may be incorrectCoarse crystalline texture with pale gray-white feldspar/quartz and rusty brown surface staining; likely Mohs 6–7, vitreous to dull luster, massive structure, and no obvious cleavage at specimen scale. The small white patch may be quartz or feldspar.
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Physical properties
Coarse crystalline texture with pale gray-white feldspar/quartz and rusty brown surface staining; likely Mohs 6–7, vitreous to dull luster, massive structure, and no obvious cleavage at specimen scale. The small white patch may be quartz or feldspar.
Formation & geological history
Formed by slow cooling of silica-rich magma deep in the crust, commonly during Precambrian to Phanerozoic intrusive events; rounded shape indicates later stream, beach, or glacial abrasion and weathering.
Uses & applications
Granite is widely used for crushed aggregate, building stone, monuments, countertops, and paving; an ordinary rounded pebble has little commercial value.
Geological facts
Iron oxidation produces the orange-brown limonite-like staining, while feldspar weathering can create the pale, chalky surface.
Field identification & locations
Identify it by visible interlocking grains of translucent/gray quartz, pale feldspar, and dark mica; unlike basalt, it is light-colored and quartz-rich. Common worldwide in granitic terrains, riverbeds, beaches, and glacial deposits.
