igneous
Vesicular basalt (scoria-like volcanic rock)
Basalt, composed mainly of plagioclase feldspar and pyroxene, commonly with olivine
AI-generated identification · may be incorrectDark gray to black and rough, with abundant small gas cavities (vesicles) and a fine-grained groundmass. Typical hardness is about 5–6 Mohs; generally dull, with no visible cleavage. The image alone does not establish its exact mineral makeup or density.
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Physical properties
Dark gray to black and rough, with abundant small gas cavities (vesicles) and a fine-grained groundmass. Typical hardness is about 5–6 Mohs; generally dull, with no visible cleavage. The image alone does not establish its exact mineral makeup or density.
Formation & geological history
Forms when low-silica lava cools rapidly at or near the surface; vesicles are bubbles trapped as gas escapes. Basalt occurs from recent eruptions to rocks billions of years old.
Uses & applications
Basalt is used as crushed aggregate, road stone, building stone, and occasionally decorative material; this small porous piece is mainly suitable for collecting or display.
Geological facts
Vesicles distinguish gas-rich volcanic rock from many dense basalts. Highly vesicular, often reddish scoria is also called volcanic cinder.
Field identification & locations
Look for a dark, fine-grained rock with rounded holes; basalt is common in volcanic regions and oceanic crust worldwide. The pictured specimen appears vesicular, but its precise identification cannot be confirmed from the photograph.
