igneous
Scoria (vesicular basalt)
Scoria; vesicular mafic volcanic rock, commonly basaltic in composition
AI-generated identification · may be incorrectHardness about 5–6 Mohs; reddish-brown to black, rough, highly vesicular, and dull to slightly glassy. It has abundant gas cavities, generally no visible cleavage, and a typical specific gravity of roughly 2.0–2.8—usually heavier than pumice.
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Physical properties
Hardness about 5–6 Mohs; reddish-brown to black, rough, highly vesicular, and dull to slightly glassy. It has abundant gas cavities, generally no visible cleavage, and a typical specific gravity of roughly 2.0–2.8—usually heavier than pumice.
Formation & geological history
Forms when gas-rich basaltic lava erupts and rapidly cools, trapping bubbles; the red-brown color commonly reflects oxidation of iron. Most examples are geologically young, ranging from recent eruptions to Cenozoic volcanic deposits.
Uses & applications
Used as lightweight aggregate, drainage material, landscaping stone, abrasive, and decorative rock; occasionally collected as a volcanic specimen. It is not typically used as a gemstone.
Geological facts
Scoria is the coarse, dark counterpart of pumice: its bubbles are larger and its walls are thicker, so it usually sinks in water. The specimen’s dense reddish texture strongly fits scoria rather than pumice.
Field identification & locations
Identify it by its irregular vesicles, low-to-moderate weight, rough surface, and volcanic red-black coloration; unlike slag, natural scoria generally lacks metallic droplets or distinctly artificial flow textures. Common around basaltic volcanic fields, including Hawaii, Iceland, Italy, and the western United States.
