igneous
Likely vesicular basalt (scoriaceous basalt)
Basalt, chiefly plagioclase feldspar, pyroxene, and commonly olivine; approximate composition 45–52% SiO₂
AI-generated identification · may be incorrectDark gray to black, fine-grained volcanic rock with elongated vesicles and a dull to slightly glassy luster; hardness about 5–6 Mohs, no obvious cleavage, and specific gravity typically 2.7–3.0. The image is somewhat blurred, so exact identification is provisional.
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Physical properties
Dark gray to black, fine-grained volcanic rock with elongated vesicles and a dull to slightly glassy luster; hardness about 5–6 Mohs, no obvious cleavage, and specific gravity typically 2.7–3.0. The image is somewhat blurred, so exact identification is provisional.
Formation & geological history
Forms when low-viscosity basaltic lava cools rapidly at or near Earth’s surface, trapping gas bubbles; most examples are Cenozoic or younger, though basalt occurs throughout geologic time. Common around shield volcanoes, lava flows, cinder cones, and oceanic crust.
Uses & applications
Used as crushed aggregate, road base, riprap, railroad ballast, and occasionally lightweight landscaping stone; generally not valuable for jewelry.
Geological facts
Vesicles distinguish it from dense basalt, while abundant holes and very low density may indicate scoria. Dark weathering rinds and tiny pale feldspar crystals are common.
Field identification & locations
Look for a black fine-grained matrix, irregular gas cavities, and a cool volcanic texture; test streak, density, and a fresh broken surface because slag or industrial material can look similar. Common worldwide, especially volcanic regions.
