igneous
Weathered basaltic rock
Basalt, likely an iron-rich, oxidized variety
AI-generated identification · may be incorrectDark reddish-brown, fine-grained, dull to weakly earthy luster with scattered lighter phenocrysts or altered patches; hardness roughly 5–6 Mohs, with no obvious cleavage. Typical composition is plagioclase, pyroxene, and iron oxides, with possible olivine alteration.
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Physical properties
Dark reddish-brown, fine-grained, dull to weakly earthy luster with scattered lighter phenocrysts or altered patches; hardness roughly 5–6 Mohs, with no obvious cleavage. Typical composition is plagioclase, pyroxene, and iron oxides, with possible olivine alteration.
Formation & geological history
Basalt forms when low-viscosity mafic lava cools rapidly at or near Earth’s surface, producing fine grains; the reddish color reflects oxidation during weathering. Most examples are Cenozoic or older, but age cannot be determined from the image.
Uses & applications
Used widely as crushed aggregate, road base, riprap, and occasionally building stone; ordinary specimens have little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Iron-bearing minerals commonly weather to red-brown hematite and limonite.
Field identification & locations
Identify it by its dense fine-grained texture, dark mafic color, and lack of visible large crystals; a streak, magnetism test, and fresh broken surface would help distinguish it from weathered sandstone or ironstone. Common in volcanic regions and ancient lava fields.
