igneous
Vesicular basalt (possibly scoriaceous basalt)
Basalt; primarily plagioclase, clinopyroxene, olivine, and iron-titanium oxides
AI-generated identification · may be incorrectDark gray to black, fine-grained, porous vesicular texture with pale weathering surfaces; typically dull to weakly glassy luster, no obvious cleavage, and Mohs hardness about 5–6. The abundant cavities formed from trapped gas bubbles, though the pale crust may reflect weathering or secondary minerals.
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Physical properties
Dark gray to black, fine-grained, porous vesicular texture with pale weathering surfaces; typically dull to weakly glassy luster, no obvious cleavage, and Mohs hardness about 5–6. The abundant cavities formed from trapped gas bubbles, though the pale crust may reflect weathering or secondary minerals.
Formation & geological history
An extrusive volcanic rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during eruptions younger than a few million years but potentially much older. Vesicles develop as dissolved gases exsolve from cooling lava.
Uses & applications
Used as crushed aggregate, road base, riprap, ballast, and occasionally lightweight landscaping stone; attractive scoria is collected but rarely used as jewelry.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust. Vesicles may later become lined or filled with zeolites, calcite, or quartz, producing amygdaloidal basalt.
Field identification & locations
Identify it by its low density, abundant rounded holes, dark mafic color, and lack of visible large crystals; a hand lens can reveal tiny plagioclase laths. Common in volcanic fields, lava flows, cinder cones, and oceanic islands.
