igneous
Weathered vesicular volcanic rock
Likely vesicular basalt or scoriaceous andesite; exact identification requires a fresh surface and tests
AI-generated identification · may be incorrectBrown-tan, highly weathered, fine-grained rock with abundant irregular vesicles and earthy to dull luster; likely hardness about 5–6 Mohs, with no visible cleavage. Vesicles indicate formerly gas-rich lava, though the apparent holes may be partly weathering cavities.
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Physical properties
Brown-tan, highly weathered, fine-grained rock with abundant irregular vesicles and earthy to dull luster; likely hardness about 5–6 Mohs, with no visible cleavage. Vesicles indicate formerly gas-rich lava, though the apparent holes may be partly weathering cavities.
Formation & geological history
Formed when mafic to intermediate lava erupted and rapidly cooled, trapping expanding gas bubbles; commonly Cenozoic to recent, but similar textures occur in older volcanic terrains. Surface oxidation and weathering produced the brown coloration.
Uses & applications
Used as lightweight aggregate, landscaping stone, and occasionally as a rough lapidary or teaching specimen; generally not jewelry-grade.
Geological facts
Vesicular basalt is often called scoria when it is dark, highly porous, and lightweight; pumice is much lighter-colored and commonly floats, so this specimen is more consistent with scoria-like basalt or andesite.
Field identification & locations
Look for a lightweight, porous texture, dark gray to reddish-brown color, and a lack of visible sedimentary layering; a streak test, density, magnetism, and a fresh broken surface would help distinguish basalt from andesite or weathered slag. Common in volcanic regions worldwide.
