igneous
Likely vesicular basalt
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase, pyroxene, and sometimes olivine
AI-generated identification · may be incorrectDark gray-brown, dull to faintly glassy, fine-grained, and irregularly vesicular or weathered; hardness about 5–6 Mohs, with no obvious cleavage and typical specific gravity around 2.8–3.0.
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Physical properties
Dark gray-brown, dull to faintly glassy, fine-grained, and irregularly vesicular or weathered; hardness about 5–6 Mohs, with no obvious cleavage and typical specific gravity around 2.8–3.0.
Formation & geological history
Forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows; specimens may range from recent eruptions to rocks hundreds of millions of years old.
Uses & applications
Used as aggregate, roadstone, railroad ballast, building stone, and occasionally as a decorative material; ordinary hand specimens have little jewelry value.
Geological facts
The porous texture may represent gas bubbles trapped during cooling, although weathering can also produce cavities. A definitive identification would require a fresh surface, streak, magnetism, or microscopic examination.
Field identification & locations
Common in volcanic regions, oceanic crust, Hawaii, Iceland, India’s Deccan Traps, and many continental lava fields; distinguish it from slag by its natural mineral texture and lack of metallic bubbles or glassy industrial appearance.
