igneous
Vesicular basalt (likely scoria)
Vesicular basalt; chiefly plagioclase, pyroxene, and often olivine
AI-generated identification · may be incorrectDark brown-gray, fine-grained, dull to weakly glassy, with abundant gas vesicles; hardness about 5–6 Mohs, no obvious cleavage, and typically ~2.3–2.8 specific gravity. Its rounded shape suggests water-worn basalt or scoria.
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Physical properties
Dark brown-gray, fine-grained, dull to weakly glassy, with abundant gas vesicles; hardness about 5–6 Mohs, no obvious cleavage, and typically ~2.3–2.8 specific gravity. Its rounded shape suggests water-worn basalt or scoria.
Formation & geological history
Formed when mafic lava cooled rapidly, trapping expanding gas bubbles; likely Cenozoic or younger, though exact age cannot be determined visually. Common in volcanic lava flows, cinder cones, and coastal or river gravels.
Uses & applications
Used as lightweight aggregate, drainage material, landscaping stone, abrasive, and occasionally as a decorative or teaching specimen; generally not gem quality.
Geological facts
Vesicles distinguish it from ordinary dense basalt; abundant, irregular pores indicate gas-rich lava. The reddish-brown color commonly results from oxidation of iron-bearing minerals.
Field identification & locations
Identify by its dark mafic color, fine texture, magnetic tendency, and numerous rounded pores; it should not fizz with dilute hydrochloric acid unless coated with carbonate. Common worldwide near volcanic regions and transported into stream or beach deposits.
