igneous
Banded vesicular basalt (likely weathered lava cobble)
Vesicular basalt, chiefly plagioclase, pyroxene, and iron-rich glass/oxides
AI-generated identification · may be incorrectDark gray to reddish-brown, fine-grained, matte to dull luster, with abundant small gas vesicles; hardness about 5–6 Mohs, no obvious cleavage, and typically specific gravity 2.7–3.0. The red zone likely reflects oxidation/weathering, while the rounded form suggests water abrasion.
Identified More igneous →
Explore Banded vesicular basalt (likely weathered lava cobble) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to reddish-brown, fine-grained, matte to dull luster, with abundant small gas vesicles; hardness about 5–6 Mohs, no obvious cleavage, and typically specific gravity 2.7–3.0. The red zone likely reflects oxidation/weathering, while the rounded form suggests water abrasion.
Formation & geological history
Formed when low-viscosity basaltic lava cooled rapidly at or near the surface, trapping gas bubbles; the reddish portion is oxidized basalt or weathering rind. Basalt ranges from Archean to modern, commonly forming volcanic flows and oceanic crust.
Uses & applications
Used as aggregate, road stone, riprap, landscaping material, and occasionally as a decorative polished stone; generally limited gemstone value.
Geological facts
Vesicles are preserved bubbles, and their abundance can indicate lava degassing conditions. The sharp color boundary may represent differential weathering, a coating, or two adjacent lava textures rather than a true compositional band.
Field identification & locations
Identify it by its heavy weight, fine texture, dark color, magnetic response in some specimens, and bubble holes; a steel file usually scratches it only with difficulty. Common in volcanic regions, river gravels, beaches, and basalt-flow landscapes.
