igneous
Vesicular basalt (possibly scoria)
Basalt; predominantly plagioclase, pyroxene, and olivine, with vesicles formed by escaping gas
AI-generated identification · may be incorrectDark gray to black, fine-grained, glassy to dull luster, irregular vesicles, and no obvious cleavage; hardness about 5–6 Mohs and specific gravity typically 2.7–3.0. The shiny surfaces may be natural glass or a polished/fractured face.
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Physical properties
Dark gray to black, fine-grained, glassy to dull luster, irregular vesicles, and no obvious cleavage; hardness about 5–6 Mohs and specific gravity typically 2.7–3.0. The shiny surfaces may be natural glass or a polished/fractured face.
Formation & geological history
An extrusive volcanic rock formed when basaltic lava cooled rapidly at or near Earth’s surface, commonly during Quaternary volcanic eruptions. Its holes are gas bubbles trapped during cooling.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, riprap, landscaping stone, and occasionally as a decorative or lapidary material.
Geological facts
The specimen may be scoria if it is unusually lightweight and highly vesicular; denser, less porous material is better termed vesicular basalt. Metallic-looking spots can be magnetite or reflective fracture surfaces.
Field identification & locations
Identify it by its black color, fine texture, abundant rounded holes, and possible weak attraction to a magnet; it should not fizz with dilute acid. Common in volcanic regions such as Hawaii, Iceland, the Cascades, and the Mediterranean.
