igneous
Vesicular basalt (scoriaceous basalt)
Basalt, chiefly plagioclase feldspar, pyroxene, and iron-titanium oxides
AI-generated identification · may be incorrectHardness about 5–6 Mohs; dark gray to black, fine-grained, dull to slightly vitreous, with abundant rounded gas vesicles and locally pale mineral-filled cavities. Typically dense overall but porous in appearance; no obvious cleavage.
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Physical properties
Hardness about 5–6 Mohs; dark gray to black, fine-grained, dull to slightly vitreous, with abundant rounded gas vesicles and locally pale mineral-filled cavities. Typically dense overall but porous in appearance; no obvious cleavage.
Formation & geological history
Forms when basaltic lava cools rapidly at or near the surface, trapping volcanic gas bubbles; specimens may be Holocene to older Cenozoic, depending on locality. Common around lava flows, cinder cones, and volcanic islands.
Uses & applications
Used as lightweight aggregate, landscaping stone, road material, and occasionally as a decorative or teaching specimen; ordinary pieces have little jewelry value.
Geological facts
Its vesicles record gas escaping from low-silica magma. Pale fillings may be calcite, zeolite, quartz, or weathered feldspar, so laboratory testing is needed for precise identification.
Field identification & locations
Identify by its black fine-grained matrix, irregular vesicles, and lack of glassy pumice-like lightness; common worldwide in volcanic regions such as Hawaii, Iceland, Japan, and the Pacific Northwest.
