igneous
Vesicular basalt
Basalt, typically composed of plagioclase feldspar, pyroxene, and minor olivine or iron oxides
AI-generated identification · may be incorrectDark gray, fine-grained, and strongly vesicular, with a dull to slightly glassy luster; hardness about 5–6 Mohs, no obvious cleavage, and typical specific gravity around 2.7–3.0.
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Physical properties
Dark gray, fine-grained, and strongly vesicular, with a dull to slightly glassy luster; hardness about 5–6 Mohs, no obvious cleavage, and typical specific gravity around 2.7–3.0.
Formation & geological history
Extrusive volcanic rock formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles. It may range from relatively young historic lava to rocks hundreds of millions of years old.
Uses & applications
Used as crushed aggregate, road base, riprap, building stone, and landscaping material; generally has little jewelry value.
Geological facts
Its holes are vesicles formed by escaping volcanic gases, and the specimen may be scoria if it is unusually light and porous. The metallic sparkle likely comes from exposed dark mineral grains or iron-bearing surfaces.
Field identification & locations
Identify it by its black-gray color, fine texture, irregular vesicles, and lack of visible large crystals; it is common in volcanic regions such as Hawaii, Iceland, the Pacific Northwest, and oceanic islands. A magnet may respond weakly because of magnetite.
