igneous
Vesicular basalt (likely weathered beach basalt)
Basalt, composed mainly of plagioclase feldspar, pyroxene, and variable olivine
AI-generated identification · may be incorrectDark gray to brown, fine-grained, porous, and dull to slightly glassy; hardness about 5–6 Mohs, with irregular fracture and no obvious cleavage. The rounded shape and cavities indicate abrasion and gas-vesicle preservation.
Identified More igneous →
Explore Vesicular basalt (likely weathered beach basalt) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to brown, fine-grained, porous, and dull to slightly glassy; hardness about 5–6 Mohs, with irregular fracture and no obvious cleavage. The rounded shape and cavities indicate abrasion and gas-vesicle preservation.
Formation & geological history
An extrusive igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface; its exact age cannot be determined from the photograph. Weathering and wave action likely rounded the specimen and enlarged some vesicles.
Uses & applications
Used as crushed aggregate, road stone, riprap, and sometimes decorative stone; this small specimen is primarily suitable for collecting or display.
Geological facts
The holes are vesicles—bubbles trapped in cooling lava—rather than sedimentary pores. Brown coloration commonly reflects oxidation and weathering of iron-bearing minerals.
Field identification & locations
Identify it by its dark fine-grained matrix, relatively high density, vesicles, and lack of visible sand grains or large crystals; common in volcanic regions and on basaltic beaches. A hand lens and streak, density, and magnetism tests can help distinguish it from vesicular slag.
