igneous
Vesicular basalt (possible scoria)
Basaltic volcanic rock; chiefly plagioclase, pyroxene, and iron-rich minerals, with vesicles formed by trapped gas
AI-generated identification · may be incorrectTypically dark gray to black, here weathered brown-purple, with rough texture and abundant cavities; dull to slightly glassy luster, fine-grained groundmass, hardness about 5–6 Mohs, no visible cleavage, and specific gravity roughly 2.6–3.0 (lower if highly vesicular).
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Physical properties
Typically dark gray to black, here weathered brown-purple, with rough texture and abundant cavities; dull to slightly glassy luster, fine-grained groundmass, hardness about 5–6 Mohs, no visible cleavage, and specific gravity roughly 2.6–3.0 (lower if highly vesicular).
Formation & geological history
Formed when basaltic lava rapidly cooled at or near Earth’s surface, allowing gas bubbles to become vesicles; likely Cenozoic or younger, though age cannot be determined from the image.
Uses & applications
Commonly used as crushed aggregate, road metal, riprap, drainage stone, and landscaping material; vesicular pieces are also collected as volcanic specimens.
Geological facts
The cavities may be empty or later lined with secondary minerals such as zeolites, calcite, or quartz. The specimen appears more basaltic than pumice because it is relatively dense and dark.
Field identification & locations
Identify by its dark fine-grained matrix, irregular gas cavities, and lack of sedimentary layering or large crystals; a magnet may respond weakly due to magnetite. Common worldwide in volcanic regions, including Hawaii, Iceland, the Cascades, and oceanic islands.
