igneous
Vesicular basalt (likely scoria)
Basaltic volcanic rock; mainly plagioclase, pyroxene, and olivine with gas vesicles
AI-generated identification · may be incorrectDark gray-brown, fine-grained, highly vesicular, and dull to slightly earthy luster; hardness about 5–6 Mohs, no visible cleavage, and typically ~2.6–2.9 specific gravity (lower if very porous).
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Physical properties
Dark gray-brown, fine-grained, highly vesicular, and dull to slightly earthy luster; hardness about 5–6 Mohs, no visible cleavage, and typically ~2.6–2.9 specific gravity (lower if very porous).
Formation & geological history
Forms when basaltic lava cools rapidly while trapped volcanic gases expand, commonly in cinder cones, lava flows, and volcanic bombs; ages range from recent eruptions to ancient volcanic terrains.
Uses & applications
Used as lightweight aggregate, landscaping stone, drainage material, and occasionally in abrasive or decorative applications; this small weathered specimen has modest collector value.
Geological facts
The holes are vesicles, originally gas bubbles frozen into the lava. Brown or reddish surfaces commonly reflect oxidation of iron-bearing minerals during or after eruption.
Field identification & locations
Identify it by its black-to-brown color, abundant irregular cavities, very fine texture, and lack of layering; it is commonly found near basaltic volcanoes, including Hawaii, Iceland, Mexico, and the western United States.
