igneous
Vesicular basalt (weathered scoriaceous basalt)
Basalt; chiefly plagioclase, pyroxene, and commonly olivine (approximately 45–52% SiO₂)
AI-generated identification · may be incorrectDark gray to reddish-brown from oxidation, with abundant rounded gas vesicles and dull to slightly earthy luster; typically fine-grained, hardness about 5–6 Mohs, and specific gravity roughly 2.7–3.0. The cavities are characteristic of scoria or vesicular basalt, though this specimen appears heavily weathered.
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Physical properties
Dark gray to reddish-brown from oxidation, with abundant rounded gas vesicles and dull to slightly earthy luster; typically fine-grained, hardness about 5–6 Mohs, and specific gravity roughly 2.7–3.0. The cavities are characteristic of scoria or vesicular basalt, though this specimen appears heavily weathered.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near the surface, trapping expanding volcanic gases; commonly Cenozoic to modern, though basalt occurs throughout Earth’s geologic history. Iron-bearing minerals weather to the reddish-brown coating.
Uses & applications
Used as crushed aggregate, road stone, riprap, lightweight construction material, and landscaping rock; attractive pieces may be collected, but it is generally not a jewelry stone.
Geological facts
Vesicles form near lava-flow surfaces where dissolved gases exsolve during decompression. The reddish coloration commonly reflects oxidation of iron in basaltic minerals.
Field identification & locations
Identify by its fine-grained dark matrix, low density relative to massive basalt, and abundant irregular cavities; distinguish it from pumice, which is usually much lighter and more silica-rich. Common in volcanic regions worldwide, including Hawaii, Iceland, the Deccan Traps, and oceanic islands.
