igneous
Vesicular basalt (scoria-like basalt)
Basalt, primarily plagioclase feldspar, pyroxene, and iron-titanium oxides
AI-generated identification · may be incorrectDark gray, fine-grained, strongly vesicular, with a dull to slightly earthy luster; hardness about 5–6 Mohs, little visible cleavage, and typical specific gravity around 2.6–2.9, reduced by the air cavities.
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Physical properties
Dark gray, fine-grained, strongly vesicular, with a dull to slightly earthy luster; hardness about 5–6 Mohs, little visible cleavage, and typical specific gravity around 2.6–2.9, reduced by the air cavities.
Formation & geological history
Formed when mafic lava rapidly cooled, trapping gas bubbles; commonly Quaternary to recent in volcanic fields, lava flows, cinder cones, and oceanic islands.
Uses & applications
Used as lightweight aggregate, landscaping stone, drainage material, and occasionally in construction; porous pieces have modest decorative or collector value.
Geological facts
The rounded cavities are vesicles formed by escaping volcanic gases. It resembles scoria, but the relatively gray, dense appearance is consistent with vesicular basalt rather than highly oxidized red scoria.
Field identification & locations
Identify it by its dark mafic color, fine texture, irregular holes, and lack of individual crystals; it is commonly found near basaltic volcanoes and volcanic beaches. A streak, magnetism test, and fresh fracture can help distinguish it from slag or pumice.
