igneous
Rounded gray pebble, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; commonly basalt (plagioclase ± pyroxene/olivine)
AI-generated identification · may be incorrectDark gray-green, dull to weakly silky, fine-grained and massive, with no obvious cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.7–3.1. Its smooth, rounded shape reflects water or beach abrasion rather than crystal form.
Identified More igneous →
Explore Rounded gray pebble, likely basalt or andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-green, dull to weakly silky, fine-grained and massive, with no obvious cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.7–3.1. Its smooth, rounded shape reflects water or beach abrasion rather than crystal form.
Formation & geological history
Likely formed when lava cooled rapidly at or near Earth’s surface, then weathered into a cobble; volcanic rocks range from ancient to recent, so age cannot be determined visually. The exact identification is uncertain without a fresh surface or testing.
Uses & applications
Used as landscaping gravel, aggregate, road material, and occasionally as a decorative or lapidary stone; this ordinary pebble has little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly contains microscopic crystals that require a hand lens to see.
Field identification & locations
Identify it by its uniform fine texture, dark gray color, lack of visible layering, and inability to scratch glass easily; a streak, magnetism test, or thin section can distinguish basalt from andesite and other stones. Common in volcanic terrains, riverbeds, beaches, and imported landscaping gravel.
