igneous
Vesicular basalt
Basalt, a mafic volcanic rock composed mainly of plagioclase feldspar, clinopyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, fine-grained, and dull to slightly vitreous; visible gas bubbles (vesicles) are typical. Hardness is about 6, with no prominent cleavage and generally high specific gravity around 2.8–3.0.
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Physical properties
Dark gray to black, fine-grained, and dull to slightly vitreous; visible gas bubbles (vesicles) are typical. Hardness is about 6, with no prominent cleavage and generally high specific gravity around 2.8–3.0.
Formation & geological history
Formed when iron- and magnesium-rich lava rapidly cooled at or near Earth’s surface, commonly in the Cenozoic or younger volcanic environments. Exact age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road base, riprap, railway ballast, building stone, and occasionally as a decorative or lapidary material. Common specimens usually have modest collector value.
Geological facts
Vesicles formed when dissolved volcanic gases expanded as pressure fell during eruption; later mineral growth may fill them, producing amygdaloidal basalt.
Field identification & locations
Common in Hawaii, Iceland, oceanic islands, mid-ocean ridges, and continental volcanic fields. Identify it by its black fine-grained texture, dense weight, and rounded or angular gas cavities; the image may also show a weathered or polished surface.
