igneous
Basalt with vesicles and possible volcanic bomb
Vesicular basalt, dominantly calcium-rich plagioclase, pyroxene, and iron-titanium oxides
AI-generated identification · may be incorrectDark gray to black, fine-grained, typically dull to weakly submetallic; hardness about 5–6 Mohs, specific gravity roughly 2.7–3.1, with irregular fracture and abundant small vesicles. The central angular clast may be a denser basaltic fragment or volcanic bomb embedded in a vesicular lava matrix.
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Physical properties
Dark gray to black, fine-grained, typically dull to weakly submetallic; hardness about 5–6 Mohs, specific gravity roughly 2.7–3.1, with irregular fracture and abundant small vesicles. The central angular clast may be a denser basaltic fragment or volcanic bomb embedded in a vesicular lava matrix.
Formation & geological history
Formed when mafic lava erupted and cooled rapidly at or near Earth’s surface, trapping gas bubbles; most examples are Cenozoic or younger, though basalt occurs throughout geological time. The texture suggests an aa-lava or scoriaceous volcanic flow/breccia.
Uses & applications
Crushed for aggregate, road base, railroad ballast, and concrete; durable varieties are used as building stone and landscaping rock. Collector value is usually low unless the specimen preserves striking volcanic textures.
Geological facts
Basalt is Earth’s most abundant volcanic rock and forms much of the oceanic crust. Vesicles may later become filled with secondary minerals such as zeolite, calcite, or quartz.
Field identification & locations
Identify it by its black color, fine texture, high density, and magnetic response from iron minerals; vesicles distinguish it from most dense intrusive rocks. Common in volcanic regions, oceanic islands, mid-ocean ridges, and continental flood-basalt provinces.
