igneous
Dark mafic rock, possibly basalt
Basalt (fine-grained mafic silicate rock; identification uncertain from image)
AI-generated identification · may be incorrectDark gray-black, rough and granular with dull to slightly glassy luster; likely composed mainly of plagioclase, pyroxene, and minor olivine. Typical basalt hardness is about Mohs 5–6, with no obvious cleavage and specific gravity around 2.8–3.0.
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Physical properties
Dark gray-black, rough and granular with dull to slightly glassy luster; likely composed mainly of plagioclase, pyroxene, and minor olivine. Typical basalt hardness is about Mohs 5–6, with no obvious cleavage and specific gravity around 2.8–3.0.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and hotspots. Specimen age cannot be determined visually; basalts range from Precambrian to modern.
Uses & applications
Used as crushed aggregate, road stone, railroad ballast, riprap, and occasionally decorative stone; ordinary rough pieces have little jewelry value.
Geological facts
The specimen’s blurry, uneven texture may also fit scoria, slag, or another dark volcanic rock; vesicles, magnetic response, and a fresh broken surface would improve identification.
Field identification & locations
Common worldwide, especially volcanic regions and oceanic islands. Field tests: basalt is typically heavy, nonmetallic, and may weakly attract a magnet; acid produces no fizz unless carbonate-filled cavities are present.
