igneous
Vesicular basalt (scoriaceous basalt)
Basalt, primarily plagioclase feldspar, clinopyroxene, and Fe-Mg minerals; locally glassy
AI-generated identification · may be incorrectDark gray to black, rough and highly vesicular, with dull to slightly glassy luster; mostly fine-grained, hardness about 5–6 Mohs, no prominent cleavage, and specific gravity typically 2.4–2.9.
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Physical properties
Dark gray to black, rough and highly vesicular, with dull to slightly glassy luster; mostly fine-grained, hardness about 5–6 Mohs, no prominent cleavage, and specific gravity typically 2.4–2.9.
Formation & geological history
Extrusive volcanic rock formed when basaltic lava cooled rapidly at or near the surface, trapping gas bubbles; commonly Quaternary to older Cenozoic, though basalt occurs throughout geologic time.
Uses & applications
Used as crushed aggregate, roadstone, riprap, and occasionally decorative stone; vesicular pieces are mainly educational or collector specimens.
Geological facts
The abundant cavities indicate gas-rich lava, but the specimen is denser and darker than typical pumice, consistent with basaltic scoria or weathered vesicular basalt.
Field identification & locations
Identify it by its black-gray color, low density relative to massive basalt, irregular vesicles, and lack of obvious sedimentary layering; common in volcanic fields, lava flows, and cinder cones worldwide.
