igneous
Vesicular basalt (possibly scoriaceous basalt)
Basalt; chiefly plagioclase feldspar, pyroxene, and iron-rich minerals
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to weakly metallic/glassy luster, with abundant elongated vesicles and weathered cavities. Hardness about 5–6 Mohs; no obvious cleavage; typically dense but porous, with irregular fracture.
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Physical properties
Dark gray to black, fine-grained, dull to weakly metallic/glassy luster, with abundant elongated vesicles and weathered cavities. Hardness about 5–6 Mohs; no obvious cleavage; typically dense but porous, with irregular fracture.
Formation & geological history
A volcanic rock formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; its exact geological age cannot be determined from the image. Common in volcanic fields, lava flows, cinder cones, and oceanic crust.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, riprap, and occasionally building stone or landscaping rock. Ordinary specimens have little jewelry value, though attractive vesicular pieces are collected.
Geological facts
The cavities are vesicles, produced by escaping dissolved gases during eruption; later mineral-filled cavities would make it amygdaloidal basalt. Its rounded form may reflect stream, beach, or glacial abrasion.
Field identification & locations
Identify by its black fine-grained matrix, lightweight porous texture, and lack of visible large crystals; distinguish it from industrial slag by its natural irregular vesicles and absence of obvious glassy flow textures or metal droplets. Common worldwide, especially Hawaii, Iceland, India, the western United States, and oceanic islands.
