igneous
Weathered basaltic rock (probable basalt)
Basalt; fine-grained mafic silicate rock, commonly plagioclase + pyroxene ± olivine
AI-generated identification · may be incorrectDark brown to olive-brown from weathering, dull earthy luster, massive and irregularly vesicular or porous; typically Mohs 5–6, with no obvious cleavage. The image alone cannot confirm mineral composition or distinguish basalt from other weathered mafic rocks.
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Physical properties
Dark brown to olive-brown from weathering, dull earthy luster, massive and irregularly vesicular or porous; typically Mohs 5–6, with no obvious cleavage. The image alone cannot confirm mineral composition or distinguish basalt from other weathered mafic rocks.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes. Brown coloration likely reflects oxidation and surface alteration of iron-bearing minerals.
Uses & applications
Used widely as crushed aggregate, road base, railroad ballast, riprap, and dimension stone; attractive polished varieties can be used decoratively. Ordinary weathered pieces usually have minimal commercial value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and forms much of the oceanic crust. Vesicles may later fill with minerals such as zeolite, calcite, or quartz.
Field identification & locations
Identify by its heavy, dense feel, dark mafic color, fine texture, and lack of visible large crystals; a streak test, hardness test, magnetism check, and thin-section or chemical analysis would improve certainty. Common worldwide in lava fields, volcanic islands, and oceanic crust.
