igneous
Vesicular basalt (weathered lava rock)
Basalt, predominantly plagioclase, clinopyroxene, and iron-magnesium minerals
AI-generated identification · may be incorrectTypically dark gray to black, fine-grained, and dull to slightly glassy; Mohs hardness about 5–6, no obvious cleavage, and moderate-to-high density. The large rounded cavities are vesicles, some likely enlarged by weathering or erosion.
Identified More igneous →
Explore Vesicular basalt (weathered lava rock) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically dark gray to black, fine-grained, and dull to slightly glassy; Mohs hardness about 5–6, no obvious cleavage, and moderate-to-high density. The large rounded cavities are vesicles, some likely enlarged by weathering or erosion.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; it may be relatively young or millions to billions of years old depending on its source. Weathering can widen vesicles and produce the rough, pitted surface.
Uses & applications
Used as landscaping stone, lightweight aggregate, riprap, drainage material, and occasionally as a decorative or sculptural specimen. Usually has limited gemstone value.
Geological facts
Vesicular basalt is commonly mistaken for slag, but natural basalt generally has an interlocking crystalline texture and irregular vesicles rather than abundant shiny glass and perfectly spherical bubbles.
Field identification & locations
Common in volcanic regions, oceanic crust, Hawaii, Iceland, western North America, and many basalt fields worldwide. Confirm with its heavy feel, dark fine-grained matrix, irregular gas cavities, and lack of metallic appearance; exact identification would benefit from a fresh broken surface or density test.
