igneous
Vesicular basalt (likely scoria)
Basaltic scoria; predominantly plagioclase, pyroxene, and olivine in a mafic volcanic glass/microcrystalline matrix
AI-generated identification · may be incorrectDark gray-black, highly vesicular, dull to slightly glassy, with irregular cavities; hardness about 5–6 Mohs, generally no visible cleavage, and specific gravity roughly 2.0–2.8 depending on vesicularity.
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Physical properties
Dark gray-black, highly vesicular, dull to slightly glassy, with irregular cavities; hardness about 5–6 Mohs, generally no visible cleavage, and specific gravity roughly 2.0–2.8 depending on vesicularity.
Formation & geological history
An extrusive igneous rock formed when gas-rich basaltic lava rapidly cooled, trapping bubbles; typically Quaternary to recent in volcanic fields, lava flows, and cinder cones.
Uses & applications
Used as lightweight aggregate, landscaping stone, abrasive material, drainage media, and occasionally in decorative rock collections; rarely used in jewelry.
Geological facts
Scoria is usually denser and darker than pumice, while basalt has a finer, less porous texture. The specimen’s porous, rough appearance strongly suggests scoria, though slag is a possible human-made look-alike.
Field identification & locations
Identify by its natural vesicles, dark mafic color, and lack of metallic sheen or uniform industrial texture; common in Hawaii, Iceland, Mexico, the western United States, and other volcanic regions.
