igneous
Vesicular basalt (likely iron-rich scoria)
Basaltic volcanic rock; chiefly plagioclase, clinopyroxene, olivine, and Fe-Ti oxides
AI-generated identification · may be incorrectDark brown-black, fine-grained, rough and strongly vesicular, with dull to locally glassy luster; hardness about 5–6, no obvious cleavage, and typical specific gravity around 2.7–3.0. The rusty surface reflects weathering of iron-bearing minerals; green patches may be moss or secondary minerals.
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Physical properties
Dark brown-black, fine-grained, rough and strongly vesicular, with dull to locally glassy luster; hardness about 5–6, no obvious cleavage, and typical specific gravity around 2.7–3.0. The rusty surface reflects weathering of iron-bearing minerals; green patches may be moss or secondary minerals.
Formation & geological history
Extrusive mafic lava cooled rapidly at or near Earth’s surface, commonly during Holocene-to-Cenozoic volcanic activity; vesicles formed from escaping gas. Exact locality and age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road base, riprap, ballast, landscaping stone, and occasionally decorative stone; uncommon as a jewelry material.
Geological facts
Its vesicles distinguish it from most dense basalt, while the heavy, dark matrix distinguishes it from pumice. The specimen appears naturally weathered rather than polished or artificially coated.
Field identification & locations
Look for a heavy black rock with small gas cavities, possible olivine crystals, and a streak that is generally gray to brown; a magnet may respond weakly because of magnetite. Common near volcanic fields, lava flows, cinder cones, and oceanic islands.
