igneous
Vesicular basalt (scoria-like volcanic rock)
Basalt, predominantly plagioclase + pyroxene ± olivine; vesicular variety
AI-generated identification · may be incorrectDark gray-brown, fine-grained and highly vesicular, with a dull to slightly earthy luster; hardness about 5–6 Mohs, no prominent cleavage, and specific gravity roughly 2.2–2.8 depending on pore space.
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Physical properties
Dark gray-brown, fine-grained and highly vesicular, with a dull to slightly earthy luster; hardness about 5–6 Mohs, no prominent cleavage, and specific gravity roughly 2.2–2.8 depending on pore space.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near the surface, with trapped gas producing the holes. Likely Cenozoic or younger, though basalt occurs from Archean to Recent volcanic settings.
Uses & applications
Common basalt is used as aggregate, road metal, riprap, and dimension stone; vesicular pieces are mainly landscaping, abrasives, or teaching and collecting specimens, with modest jewelry use.
Geological facts
The rounded holes are vesicles, not fossils; their abundance indicates gas-rich lava. The pictured piece may also be weathered scoria or porous basaltic construction aggregate.
Field identification & locations
Identify it by its dark color, very fine texture, heavy feel, and abundant irregular vesicles; it is commonly found in lava flows, cinder cones, volcanic fields, and crushed-stone surfaces worldwide.
