igneous
Likely basaltic volcanic rock
Basalt, chiefly plagioclase feldspar and clinopyroxene, with possible olivine or iron oxides
AI-generated identification · may be incorrectDark gray-black, fine-grained and uneven, with dull to weakly vitreous luster; typical hardness is about Mohs 5–6, no obvious cleavage, and density about 2.8–3.0 g/cm³. The specimen may be vesicular or weathered, but the image is insufficient for a definitive identification.
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Physical properties
Dark gray-black, fine-grained and uneven, with dull to weakly vitreous luster; typical hardness is about Mohs 5–6, no obvious cleavage, and density about 2.8–3.0 g/cm³. The specimen may be vesicular or weathered, but the image is insufficient for a definitive identification.
Formation & geological history
Basalt forms when low-silica mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and hotspot regions. Its age could range from recent volcanic material to billions of years.
Uses & applications
Used widely as crushed aggregate, road stone, railway ballast, building stone, and occasionally as a polished decorative material. Ordinary hand specimens have little commercial value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. It commonly contains microscopic crystals that require a hand lens or microscope to resolve.
Field identification & locations
Look for a dark, dense, fine-grained texture and possible tiny vesicles; a streak, magnetism, and acid test can help distinguish it from slag or other dark rocks. Common localities include Hawaii, Iceland, the Deccan Traps, and oceanic volcanic terrains.
