igneous
Vesicular basalt (scoria-like volcanic rock)
Vesicular basalt; commonly composed of plagioclase, pyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectDark brown to gray, highly porous, dull to slightly glassy, with abundant gas vesicles; hardness about 5–6 Mohs, no prominent cleavage, and typical specific gravity around 2.4–2.8 (lower when vesicular).
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Physical properties
Dark brown to gray, highly porous, dull to slightly glassy, with abundant gas vesicles; hardness about 5–6 Mohs, no prominent cleavage, and typical specific gravity around 2.4–2.8 (lower when vesicular).
Formation & geological history
Forms when gas-rich basaltic lava cools rapidly at or near the surface, trapping bubbles; generally Quaternary to modern in age and associated with cinder cones, lava flows, and volcanic fields.
Uses & applications
Used as lightweight aggregate, landscaping stone, drainage material, and occasionally as an abrasive or decorative specimen; usually low jewelry value.
Geological facts
The irregular holes are vesicles formed by escaping volcanic gases, and weathering can enlarge them. Its brown coloration may reflect oxidation of iron-bearing minerals.
Field identification & locations
Identify it by its black-to-brown basaltic color, very high vesicularity, rough texture, and lack of layering; common worldwide in volcanic regions such as Hawaii, Iceland, Mexico, Italy, and the western United States.
