igneous
Vesicular basalt (scoria-like volcanic rock)
Vesicular basalt; primarily plagioclase, pyroxene, and olivine with iron-rich volcanic glass
AI-generated identification · may be incorrectDark reddish-brown, porous, dull to slightly vitreous luster, with abundant gas vesicles; typically hardness 5–6 Mohs, massive texture, no cleavage, and specific gravity about 2.4–2.9 (lower when highly vesicular).
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Physical properties
Dark reddish-brown, porous, dull to slightly vitreous luster, with abundant gas vesicles; typically hardness 5–6 Mohs, massive texture, no cleavage, and specific gravity about 2.4–2.9 (lower when highly vesicular).
Formation & geological history
Formed when mafic lava cooled rapidly at or near the surface, trapping expanding gas bubbles; commonly Quaternary to recent in age, though older examples occur widely.
Uses & applications
Used as lightweight aggregate, landscaping stone, refractory material, and occasionally as a mineral-collection specimen; generally has little jewelry value.
Geological facts
The reddish color commonly results from oxidation of iron-bearing minerals during or after emplacement. Its vesicles distinguish it from dense basalt and pumice, which is usually much lighter and paler.
Field identification & locations
Identify it by its dense, dark mafic composition, reddish weathering, irregular vesicles, and lack of layering; common in volcanic regions such as Hawaii, Iceland, the Pacific Northwest, Italy, and Mexico. Estimated value: $2–$15 for a common hand specimen, or up to $25–$50 if unusually attractive or locality-labeled.
