igneous
Rounded basalt pebble
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, with possible olivine
AI-generated identification · may be incorrectDark gray-green, dull to weakly granular, and smoothly water-worn; typically Mohs hardness 5–6, dense, with very fine crystals and no obvious cleavage. The image is insufficient to confirm exact mineralogy.
Identified More igneous →
Explore Rounded basalt pebble 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 granular, and smoothly water-worn; typically Mohs hardness 5–6, dense, with very fine crystals and no obvious cleavage. The image is insufficient to confirm exact mineralogy.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes; its rounded shape indicates stream, beach, or glacial transport.
Uses & applications
Used as crushed aggregate, road base, riprap, railroad ballast, and occasionally decorative stone; this small pebble has negligible commercial value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms seafloor lava flows, including pillow basalts.
Field identification & locations
Look for a dark, heavy, fine-grained rock that does not fizz with dilute acid and may show tiny vesicles or scattered olivine grains. Common worldwide in volcanic terrains and alluvial gravels.
