igneous
Vesicular basalt (pumice-like volcanic stone)
Vesicular basalt; primarily plagioclase, pyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectHardness about 5–6 Mohs; light gray, fine-grained, dull to faintly satin luster, with abundant rounded gas vesicles. It is dense-to-moderately porous and lacks obvious cleavage; the smooth shape suggests weathering or water abrasion.
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Physical properties
Hardness about 5–6 Mohs; light gray, fine-grained, dull to faintly satin luster, with abundant rounded gas vesicles. It is dense-to-moderately porous and lacks obvious cleavage; the smooth shape suggests weathering or water abrasion.
Formation & geological history
Formed when gas-rich basaltic lava cooled rapidly, trapping bubbles; likely Cenozoic or younger, though the exact age cannot be determined visually. Its rounded form indicates transport by waves or streams.
Uses & applications
Used as lightweight aggregate, landscaping stone, abrasive, and occasionally in decorative specimens; generally not a jewelry gemstone.
Geological facts
Unlike true pumice, basaltic vesicular rock is usually heavier and darker because its bubbles occur in a crystalline mafic matrix. Surface pits may also be enlarged by weathering.
Field identification & locations
Identify it by its gray mafic color, numerous cavities, and lack of sedimentary layering or fossil structure; common in volcanic regions and beaches near basalt flows. A hand lens and density test help distinguish it from concrete or coral.
