igneous
Vesicular basalt (scoria-like volcanic rock)
Basalt, chiefly plagioclase feldspar, pyroxene, and iron-rich minerals; abundant vesicles from escaping volcanic gas
AI-generated identification · may be incorrectHardness about 5–6 Mohs; brown-gray to reddish, dull to slightly earthy luster, fine-grained groundmass, and highly porous vesicular texture. No obvious cleavage; typically dense overall but lightweight relative to solid basalt.
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Physical properties
Hardness about 5–6 Mohs; brown-gray to reddish, dull to slightly earthy luster, fine-grained groundmass, and highly porous vesicular texture. No obvious cleavage; typically dense overall but lightweight relative to solid basalt.
Formation & geological history
Forms when basaltic lava cools rapidly at or near a volcanic vent, trapping gas bubbles; generally Cenozoic or younger, though similar rocks occur throughout geologic time. The specimen may be scoria, especially if strongly oxidized and unusually porous.
Uses & applications
Used as lightweight aggregate, landscaping stone, abrasive, and horticultural soil amendment; occasionally collected as a volcanic specimen. It has little jewelry value.
Geological facts
Vesicles are usually gas cavities rather than mineral crystals; reddish coloration commonly reflects oxidation of iron-bearing minerals. Scoria is generally darker and heavier than pumice, while pumice is often pale and exceptionally lightweight.
Field identification & locations
Identify by its rough, bubbly surface, dark mafic composition, and lack of layering or fossils; a streak test, density, and lack of reaction to dilute acid help distinguish it from porous limestone. Common near basaltic volcanoes, including Hawaii, Iceland, Mexico, and the western United States.
