igneous
Vesicular basalt
Basalt, predominantly plagioclase feldspar, pyroxene, and olivine; vesicles may contain secondary minerals
AI-generated identification · may be incorrectDark gray to black, fine-grained, matte to slightly vitreous, with abundant gas vesicles; hardness about 5–6 Mohs, massive texture, generally no visible cleavage, and specific gravity roughly 2.7–3.0.
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Physical properties
Dark gray to black, fine-grained, matte to slightly vitreous, with abundant gas vesicles; hardness about 5–6 Mohs, massive texture, generally no visible cleavage, and specific gravity roughly 2.7–3.0.
Formation & geological history
An extrusive volcanic rock formed when basaltic lava cooled rapidly at or near Earth’s surface, commonly during Quaternary or older volcanic eruptions. Vesicles formed from trapped gas bubbles during solidification.
Uses & applications
Used as crushed aggregate, road base, drainage stone, riprap, and landscaping material; attractive polished or vesicular pieces are also sold as display specimens.
Geological facts
Basalt is Earth’s most common volcanic rock and forms much of the oceanic crust. Its vesicles distinguish it from many dense dark rocks, though slag can look similar.
Field identification & locations
Identify by its black, fine-grained groundmass, high density, and rounded or elongated pores; it is typically nonmagnetic to weakly magnetic. Common sources include Hawaii, Iceland, the Columbia River Basalt Province, India, and other volcanic regions.
