igneous
Vesicular basalt (scoria-like volcanic rock)
Basalt, a mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and minor olivine
AI-generated identification · may be incorrectDark gray to black, highly vesicular, dull to slightly glassy luster; typically fine-grained with no visible crystals. Mohs hardness about 5–6, no cleavage, and specific gravity commonly 2.4–3.0 (lower when very porous).
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Physical properties
Dark gray to black, highly vesicular, dull to slightly glassy luster; typically fine-grained with no visible crystals. Mohs hardness about 5–6, no cleavage, and specific gravity commonly 2.4–3.0 (lower when very porous).
Formation & geological history
Formed when gas-rich basaltic lava cooled rapidly at or near Earth’s surface, trapping bubbles; generally Cenozoic or younger, though basalt occurs throughout geologic time.
Uses & applications
Used as lightweight aggregate, landscaping stone, abrasives, and occasionally architectural stone; collectible interest is modest unless unusually shaped or locality-specific.
Geological facts
The holes are vesicles formed by escaping volcanic gases; abundant vesicles indicate scoria or vesicular basalt rather than dense basalt.
Field identification & locations
Identify by its black-gray color, rough frothy texture, and abundant irregular cavities; common in volcanic regions such as Hawaii, Iceland, the western United States, and oceanic islands. It is not pumice if it is dark, dense, and does not readily float.
