igneous
Likely polished basalt with pale mineral inclusions
Basalt; inclusions possibly calcite, quartz, or weathered feldspar
AI-generated identification · may be incorrectSmall, rounded, polished dark-gray to black pebble with a dull-to-subvitreous surface and irregular cream-colored patches. Basalt typically has fine-grained interlocking crystals, Mohs hardness about 5–6, no obvious cleavage, and specific gravity around 2.8–3.0;…
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Physical properties
Small, rounded, polished dark-gray to black pebble with a dull-to-subvitreous surface and irregular cream-colored patches. Basalt typically has fine-grained interlocking crystals, Mohs hardness about 5–6, no obvious cleavage, and specific gravity around 2.8–3.0; the inclusions cannot be identified reliably from this image alone.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface. The pale spots may represent amygdules later filled by calcite or silica, or lighter altered minerals; basalt is generally Cenozoic or older depending on its source.
Uses & applications
Used widely as crushed aggregate, road stone, building stone, and decorative polished material. This small piece has modest specimen or craft value.
Geological facts
The smooth oval shape indicates natural water wear and/or tumbling. Its appearance is also compatible with a basaltic pebble containing light vesicle fillings, rather than a single crystal mineral.
Field identification & locations
Common in glacially transported deposits around southern Michigan/northern Indiana, including the reported region, though it is not necessarily locally formed. Check with a magnet, streak, and vinegar: basalt may be weakly magnetic; calcite fillings fizz weakly with acid. Avoid calling it meteorite—its rounded black appearance alone is insufficient.
