igneous
Vesicular basalt (lava rock)
Vesicular basalt, a basaltic volcanic rock composed mainly of plagioclase, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to slightly glassy surface with rounded gas cavities (vesicles); constituent minerals are typically Mohs 5–6, and the rock has no consistent cleavage. The specimen appears water-worn and rounded.
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Physical properties
Dark gray-brown, fine-grained, dull to slightly glassy surface with rounded gas cavities (vesicles); constituent minerals are typically Mohs 5–6, and the rock has no consistent cleavage. The specimen appears water-worn and rounded.
Formation & geological history
Formed when gas-rich basaltic lava cooled quickly, trapping bubbles; basalt is common from recent volcanism through much of Earth’s geological history. The image alone cannot establish its age or exact source.
Uses & applications
Basalt is used as crushed aggregate, road stone, and building material; vesicular pieces are also collected or used decoratively and in landscaping.
Geological facts
The holes are vesicles left by gas bubbles escaping or trapped during cooling; abundant vesicles make basalt lighter and more porous than solid basalt.
Field identification & locations
Look for a dark, fine-grained matrix with irregular rounded cavities; distinguish it from pumice, which is usually much lighter and more densely vesicular. Vesicular basalt occurs in volcanic regions worldwide.
