igneous
Vesicular basalt (probable scoriaceous basalt)
Basalt; chiefly plagioclase, clinopyroxene, and iron-titanium oxides, with possible olivine
AI-generated identification · may be incorrectDark reddish-brown, fine-grained, porous, and dull to slightly earthy; likely Mohs 5–6, with no visible cleavage. The reddish color commonly reflects oxidation of iron-bearing minerals, while cavities indicate vesicles formed by escaping gas.
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Physical properties
Dark reddish-brown, fine-grained, porous, and dull to slightly earthy; likely Mohs 5–6, with no visible cleavage. The reddish color commonly reflects oxidation of iron-bearing minerals, while cavities indicate vesicles formed by escaping gas.
Formation & geological history
An extrusive volcanic rock produced when mafic lava cooled rapidly at or near the surface, probably during a relatively young volcanic eruption; its exact age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road base, railway ballast, concrete additive, and decorative stone; attractive vesicular pieces are collected but generally have modest value.
Geological facts
The holes are gas bubbles frozen into the lava, distinguishing scoriaceous basalt from dense basalt. Red coloration may develop during eruption or later weathering in an oxygen-rich environment.
Field identification & locations
Common in volcanic regions such as Hawaii, Iceland, the western United States, Japan, and oceanic islands. Confirm with a fresh surface, magnetism, lack of acid reaction, and a hardness sufficient to scratch glass; exact identification requires testing.
