igneous
Probable rough basalt or mafic igneous fragment
Fine-grained basalt, likely plagioclase–pyroxene–olivine aggregate
AI-generated identification · may be incorrectDark gray to black, irregular and fine-grained with a dull to weakly glassy luster; typical hardness is about 5–6 Mohs, with no obvious cleavage and specific gravity around 2.8–3.0. The image is somewhat blurred, so mineral identification is provisional.
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Physical properties
Dark gray to black, irregular and fine-grained with a dull to weakly glassy luster; typical hardness is about 5–6 Mohs, with no obvious cleavage and specific gravity around 2.8–3.0. The image is somewhat blurred, so mineral identification is provisional.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. Most examples are geologically young relative to Earth’s history, though basalt occurs from Archean to modern ages.
Uses & applications
Used as crushed aggregate, roadstone, riprap, railway ballast, and occasionally as a decorative stone; ordinary hand specimens have little commercial value.
Geological facts
Basalt is the most abundant volcanic rock and commonly contains microscopic crystals, making individual minerals difficult to see without magnification.
Field identification & locations
Look for a dense, dark, non-layered rock that does not fizz with dilute acid; a streak, fresh fracture, magnet test, and hand lens help distinguish it from slag or meteorite material. Common worldwide, especially volcanic regions and ocean beaches.
