igneous
Vesicular basalt
Basalt, a mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained groundmass with abundant rounded gas vesicles and scattered reddish-brown alteration minerals; typically dull to weakly vitreous, hardness about 5–6, no obvious cleavage, and specific gravity approximately 2.7–3.0.
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Physical properties
Dark gray-brown, fine-grained groundmass with abundant rounded gas vesicles and scattered reddish-brown alteration minerals; typically dull to weakly vitreous, hardness about 5–6, no obvious cleavage, and specific gravity approximately 2.7–3.0.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping volcanic gases as vesicles; likely Cenozoic or younger, though basalt occurs throughout geologic time in volcanic flows, oceanic crust, and volcanic islands.
Uses & applications
Used as crushed aggregate, road stone, riprap, railroad ballast, and occasionally architectural stone; vesicular varieties are also collected as volcanic specimens or used as lightweight landscaping rock.
Geological facts
The holes are gas bubbles, not fossils; reddish patches commonly represent oxidized iron-bearing minerals or weathering. It may resemble scoria, but basalt generally has a denser, finer-grained matrix.
Field identification & locations
Identify it by its dark mafic color, fine texture, and vesicles; common worldwide in lava fields, volcanic islands, and oceanic crust. A magnet may show weak attraction if magnetite is present.
