igneous
Rounded gray river cobble, likely quartz-rich sandstone or weathered granite
Indeterminate; possible granitic or feldspathic cobble (quartz–feldspar–mica aggregate)
AI-generated identification · may be incorrectPale gray-beige, dull to slightly granular luster, massive and rounded with no obvious cleavage or crystals; estimated Mohs hardness 6–7 if granite/quartz-rich rock, with moderate-to-high density.
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Physical properties
Pale gray-beige, dull to slightly granular luster, massive and rounded with no obvious cleavage or crystals; estimated Mohs hardness 6–7 if granite/quartz-rich rock, with moderate-to-high density.
Formation & geological history
Natural abrasion in a stream, beach, or glacial environment rounded the specimen; the original rock likely formed deep in the crust as an intrusive igneous rock, commonly hundreds of millions to billions of years old.
Uses & applications
Typically used as landscaping stone, garden rock, or a curiosity; it has little jewelry or industrial value unless cutting reveals attractive texture or veining.
Geological facts
The smooth shape indicates prolonged transport or tumbling, while the subtle speckling and hard surface are consistent with quartz-bearing material. Exact identification requires a fresh broken surface, hand lens, streak, and acid testing.
Field identification & locations
Look for visible quartz grains, pink/white feldspar, and dark mica to confirm granite; a dilute hydrochloric-acid reaction would suggest carbonate rock instead. Common as stream cobbles worldwide.
