igneous
Vesicular basalt (likely weathered volcanic rock)
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to brown, fine-grained and locally vesicular, with dull to slightly glassy luster; Mohs hardness about 5–6, no prominent cleavage, and specific gravity roughly 2.7–3.0. The pale surface may reflect weathering or mineral coating.
Identified More igneous →
Explore Vesicular basalt (likely weathered volcanic rock) 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 and locally vesicular, with dull to slightly glassy luster; Mohs hardness about 5–6, no prominent cleavage, and specific gravity roughly 2.7–3.0. The pale surface may reflect weathering or mineral coating.
Formation & geological history
An extrusive igneous rock formed when low-silica lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic activity. Vesicles formed from gas bubbles trapped in the lava.
Uses & applications
Used as crushed aggregate, road metal, riprap, railroad ballast, and building stone; attractive polished varieties may be used decoratively. This rough specimen has minimal commercial value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of oceanic crust. Vesicular basalt can resemble scoria, but scoria is typically more porous, reddish, and strongly glassy.
Field identification & locations
Look for a heavy, fine-grained dark rock with tiny cavities and no visible large crystals; it should not fizz with dilute hydrochloric acid unless coated with carbonate. Common in volcanic regions, including Hawaii, Iceland, the Pacific Northwest, and oceanic islands.
