igneous
Possible weathered basalt or slag fragment
Basalt, chiefly plagioclase and pyroxene; identification is uncertain from the image
AI-generated identification · may be incorrectDark black, rough, irregular, and likely fine-grained; basalt has Mohs hardness about 6, dull to slightly glassy luster, no visible cleavage, and specific gravity about 2.8–3.0. Vesicles or a glassy texture could indicate industrial slag instead.
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Physical properties
Dark black, rough, irregular, and likely fine-grained; basalt has Mohs hardness about 6, dull to slightly glassy luster, no visible cleavage, and specific gravity about 2.8–3.0. Vesicles or a glassy texture could indicate industrial slag instead.
Formation & geological history
If natural, basalt formed when mafic lava cooled rapidly at or near Earth’s surface, ranging from ancient to modern ages. Its isolated, very dark appearance on a pebble-rich paved surface could also represent asphalt, coal, or man-made slag rather than a geological specimen.
Uses & applications
Basalt is widely used as crushed aggregate, road stone, building stone, and occasionally in decorative work. Small unidentified fragments generally have negligible commercial or collector value.
Geological facts
The surrounding material appears to be concrete or asphalt aggregate, and the black object may be embedded debris rather than a loose specimen. A fresh broken surface and close inspection for vesicles, metallic beads, or glassiness would improve identification.
Field identification & locations
Check for a fine crystalline texture, scattered pale plagioclase, magnetic response, and a clean stony fracture; slag often has abundant bubbles, glassy surfaces, or metal-like inclusions. Common basalt sources include volcanic regions worldwide.
