igneous
Dark fine-grained rock, possibly basalt
Basalt (tentative identification; image alone is insufficient for certainty)
AI-generated identification · may be incorrectBlack to dark gray, dull to slightly glassy, with a rough, fine-grained surface and irregular fracture. Basalt is typically composed of plagioclase and pyroxene, sometimes olivine; hardness is about 6 on the Mohs scale.
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Physical properties
Black to dark gray, dull to slightly glassy, with a rough, fine-grained surface and irregular fracture. Basalt is typically composed of plagioclase and pyroxene, sometimes olivine; hardness is about 6 on the Mohs scale.
Formation & geological history
Basalt forms when mafic lava cools quickly at or near Earth’s surface; its age cannot be determined from the image.
Uses & applications
Commonly used as crushed aggregate for roads and concrete, building stone, and landscaping material.
Geological facts
Basalt is one of Earth’s most widespread volcanic rocks and also forms much of the ocean floor.
Field identification & locations
Look for a dense, dark rock with grains too small to see unaided; compare streak, heft, and texture, since slag and other dark rocks can look similar. Basalt occurs worldwide in volcanic regions and old lava flows.
