igneous
Vesicular basalt (scoriaceous basalt)
Basalt, primarily plagioclase, pyroxene, and iron-rich olivine; vesicular variety may be termed scoria
AI-generated identification · may be incorrectDark reddish-brown, fine-grained and porous with abundant small vesicles; typically dull to slightly glassy, hardness about 5–6 Mohs, no obvious cleavage, and specific gravity roughly 2.4–2.9 (lower if highly vesicular).
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Physical properties
Dark reddish-brown, fine-grained and porous with abundant small vesicles; typically dull to slightly glassy, hardness about 5–6 Mohs, no obvious cleavage, and specific gravity roughly 2.4–2.9 (lower if highly vesicular).
Formation & geological history
Forms when mafic lava cools rapidly at or near the surface, with escaping gas producing the cavities; commonly associated with young volcanic flows, cinder cones, and lava fields, ranging from recent to Precambrian in age.
Uses & applications
Used as lightweight aggregate, landscaping stone, road material, and occasionally abrasive or decorative rock; ordinary pieces have little jewelry value.
Geological facts
The rusty color usually reflects oxidation of iron-bearing minerals after exposure; its vesicles distinguish it from dense basalt and may contain secondary minerals such as zeolites or calcite.
Field identification & locations
Field identification relies on its rough, porous texture, dark mafic color, high density relative to pumice, and lack of visible large crystals; common worldwide in volcanic regions such as Hawaii, Iceland, Mexico, and the western United States.
