igneous
Likely basalt
Basalt; fine-grained mafic volcanic rock, mainly plagioclase and pyroxene, commonly with olivine
AI-generated identification · may be incorrectDark gray, uneven and apparently fine-grained with a subtle sparkle; typical basalt has Mohs hardness around 6, a dull to slightly vitreous luster, and no prominent cleavage. The image’s texture and scale are insufficient to confirm the identification.
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Physical properties
Dark gray, uneven and apparently fine-grained with a subtle sparkle; typical basalt has Mohs hardness around 6, a dull to slightly vitreous luster, and no prominent cleavage. The image’s texture and scale are insufficient to confirm the identification.
Formation & geological history
Forms when iron- and magnesium-rich lava cools quickly at or near the surface. Basalt occurs in rocks of many ages, from recent eruptions to ancient volcanic provinces.
Uses & applications
Widely used as crushed aggregate for roads and concrete, dimension stone, and occasionally decorative or landscape material.
Geological facts
Basalt is the most common volcanic rock in Earth’s oceanic crust and forms extensive lava plateaus and seafloor flows.
Field identification & locations
A dark, dense specimen with fine crystals and no visible layering is consistent with basalt; inspect a fresh surface for tiny plagioclase laths or olivine grains. Common worldwide at volcanoes and in oceanic crust; the pictured specimen cannot be identified reliably from appearance alone.
