igneous
Dark vesicular volcanic rock, likely basalt
Basalt (predominantly plagioclase and pyroxene, with possible olivine and iron oxides)
AI-generated identification · may be incorrectDark gray-black, fine-grained, dull to slightly vitreous; likely Mohs hardness 5–6, massive texture, and no obvious cleavage. The irregular pale-brown rim may be weathering, attached soil, or a vesicular/altered surface.
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Physical properties
Dark gray-black, fine-grained, dull to slightly vitreous; likely Mohs hardness 5–6, massive texture, and no obvious cleavage. The irregular pale-brown rim may be weathering, attached soil, or a vesicular/altered surface.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields, lava flows, and oceanic crust. Its exact age cannot be determined from the photograph; basalt ranges from ancient to geologically recent.
Uses & applications
Commonly used as crushed aggregate, road stone, railway ballast, riprap, and building stone; attractive pieces may be collected but this specimen has little gem value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly contains abundant iron and magnesium minerals. Vesicles, if present, formed from gas bubbles trapped during lava cooling.
Field identification & locations
Identify it by its dense black fine-grained appearance, heavy weight, and lack of visible large crystals; a streak, magnetism, and fresh broken surface would help distinguish basalt from slag or weathered concrete. Common localities include volcanic regions, oceanic islands, and ancient lava provinces.
