igneous
Vesicular basalt (possibly industrial slag)
Basalt, chiefly plagioclase + pyroxene ± olivine; exact identification is uncertain from the image
AI-generated identification · may be incorrectDark gray, fine-grained, dull to weakly metallic weathered surface with abundant rounded vesicles; likely Mohs 5–6, massive with no obvious cleavage. The unusually metallic-looking crust and angular shape could indicate iron-rich furnace slag rather than natural basalt.
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Physical properties
Dark gray, fine-grained, dull to weakly metallic weathered surface with abundant rounded vesicles; likely Mohs 5–6, massive with no obvious cleavage. The unusually metallic-looking crust and angular shape could indicate iron-rich furnace slag rather than natural basalt.
Formation & geological history
Natural basalt forms when basaltic lava rapidly cools at or near Earth’s surface, commonly during volcanic eruptions; ages range from modern to Archean. Slag forms artificially during metal smelting and may contain trapped gas bubbles and iron oxides.
Uses & applications
Basalt is used as crushed aggregate, paving stone, and building material; attractive varieties are decorative. Slag is mainly used as aggregate or cement additive, with little jewelry value.
Geological facts
Natural basalt vesicles may contain secondary minerals such as zeolite, calcite, or quartz. Smooth flow-like metal patches, sharp molded edges, magnetic response, and glassy areas favor slag.
Field identification & locations
Test for strong magnetism, streak, density, and fresh fracture; a microscope or chemical analysis is needed for certainty. Common basalt occurs in volcanic regions worldwide; industrial slag is found near historic furnaces and smelters.
