igneous
Vesicular basalt (scoria-like volcanic rock)
Basalt; primarily plagioclase feldspar, pyroxene, and olivine (variable)
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to slightly vitreous, with abundant irregular vesicles (gas bubbles); typically Mohs 5–6 and specific gravity about 2.7–3.0. It is usually massive, with no prominent cleavage, though individual minerals may show cleavage.
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Physical properties
Dark gray to black, fine-grained, dull to slightly vitreous, with abundant irregular vesicles (gas bubbles); typically Mohs 5–6 and specific gravity about 2.7–3.0. It is usually massive, with no prominent cleavage, though individual minerals may show cleavage.
Formation & geological history
An extrusive mafic igneous rock formed when basaltic lava cooled rapidly at or near the surface, trapping volcanic gases. Its exact geological age cannot be determined from the image; basalt forms from Precambrian to modern volcanic activity.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, riprap, and building stone; attractive vesicular pieces may be collected or used decoratively.
Geological facts
The holes are vesicles, not fossils, and indicate gas-rich lava. Dense basalt is heavier than similarly sized pumice; highly vesicular varieties may be called scoria.
Field identification & locations
Common in volcanic regions, including Hawaii, Iceland, Japan, the Columbia River Plateau, and oceanic islands. Identify it by its black fine-grained matrix, weight, and bubble cavities; a streak test is usually gray-black.
