igneous
Weathered basalt pebble with a vesicle
Basalt (fine-grained mafic volcanic rock; commonly plagioclase, clinopyroxene, and Fe-Mg oxides)
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to weakly vitreous surface, with one rounded cavity (vesicle) containing dark material; typical hardness about 5–6 Mohs and specific gravity about 2.8–3.0. The rounded shape indicates water or sediment abrasion.
Identified More igneous →
Explore Weathered basalt pebble with a vesicle in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-brown, fine-grained, dull to weakly vitreous surface, with one rounded cavity (vesicle) containing dark material; typical hardness about 5–6 Mohs and specific gravity about 2.8–3.0. The rounded shape indicates water or sediment abrasion.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, likely in the Cenozoic or older depending on locality; the cavity formed from trapped gas bubbles and later weathering or mineral infill.
Uses & applications
Common basalt is used as aggregate, road stone, riprap, building stone, and occasionally decorative material; this small weathered piece has little commercial value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and forms much of oceanic crust. Vesicles may later fill with zeolites, calcite, quartz, or chalcedony.
Field identification & locations
Identify it by its heavy, fine-grained dark body, lack of visible large crystals, and vesicle; a magnet may respond weakly because of magnetite. Common in volcanic regions, river gravels, beaches, and glacial deposits.
