igneous
Weathered basalt or dark igneous rock fragment
Likely basalt, a fine-grained mafic volcanic rock; exact identification is uncertain from the image
AI-generated identification · may be incorrectDark gray-brown, rough and irregular with a dull-to-subtle granular luster; likely hardness about 5–6 Mohs, composed mainly of plagioclase feldspar and pyroxene, with possible olivine. Cleavage is not obvious and the specimen appears heavily weathered.
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Physical properties
Dark gray-brown, rough and irregular with a dull-to-subtle granular luster; likely hardness about 5–6 Mohs, composed mainly of plagioclase feldspar and pyroxene, with possible olivine. Cleavage is not obvious and the specimen appears heavily weathered.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Its age cannot be determined visually; this may also be a weathered landscaping or construction fragment.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, riprap, and occasionally ornamental stone; this small weathered piece has little commercial value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms dark lava flows, including columnar-jointed cliffs.
Field identification & locations
A dense, dark, fine-grained texture and lack of visible large crystals support basalt; test for hardness and streak, and check whether it is magnetic or vesicular. Common worldwide, especially near volcanic regions.
