igneous
Possible basalt or volcanic scoria fragment
Mafic volcanic rock, likely basalt; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectDark black, fine-grained to weakly vesicular, with a rough uneven surface and dull to slightly vitreous luster. Basalt typically has Mohs hardness 5–6, no obvious cleavage, and specific gravity about 2.8–3.0; the specimen may contain iron-oxide staining or weathering pits.
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Physical properties
Dark black, fine-grained to weakly vesicular, with a rough uneven surface and dull to slightly vitreous luster. Basalt typically has Mohs hardness 5–6, no obvious cleavage, and specific gravity about 2.8–3.0; the specimen may contain iron-oxide staining or weathering pits.
Formation & geological history
Likely formed when iron- and magnesium-rich lava rapidly cooled at or near Earth’s surface, commonly during Cenozoic or younger volcanic activity. Its small, irregular form could also represent weathered scoria or industrial slag, which cannot be excluded visually.
Uses & applications
Basalt is widely used as crushed aggregate, road stone, riprap, and occasionally building stone; attractive pieces may be collected. Small common specimens generally have little commercial value.
Geological facts
Basalt commonly contains plagioclase, pyroxene, and sometimes olivine; vesicles indicate gas bubbles trapped during cooling. A magnet test may show attraction if magnetite is abundant.
Field identification & locations
Look for a uniformly fine texture, natural vesicles, and gray-black color; a glassy, flow-banded surface, metallic droplets, or unusually lightweight porous texture would suggest slag instead. Common worldwide, especially near volcanic regions.
