igneous
Possible industrial slag or basaltic volcanic glass
Likely iron-rich vitreous slag; natural alternative: basaltic glass (tachylite)
AI-generated identification · may be incorrectDark gray-black, glassy to metallic luster, vesicular and irregularly fractured; apparent hardness about 5–6, with no visible cleavage. Numerous rounded cavities and shiny metallic particles favor slag over a natural mineral specimen.
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Physical properties
Dark gray-black, glassy to metallic luster, vesicular and irregularly fractured; apparent hardness about 5–6, with no visible cleavage. Numerous rounded cavities and shiny metallic particles favor slag over a natural mineral specimen.
Formation & geological history
Most likely a human-processed byproduct of metal smelting, formed when molten furnace material rapidly cooled; it has no meaningful geological age. If natural, it could be rapidly quenched basaltic lava, generally Cenozoic or younger.
Uses & applications
Industrial slag is used in aggregate, cement, and abrasives but has little gem or collector value; basaltic glass is mainly a geological collectible and occasionally an abrasive material.
Geological facts
The bubbly texture, flow-like glass, metallic inclusions, and sharply irregular edges are characteristic of furnace slag. Natural volcanic glass more commonly shows uniform composition and lacks conspicuous metal droplets.
Field identification & locations
Test with a magnet, streak, and specific gravity: strong magnetism, gray streak, and unusually heavy weight support iron slag. Common around historic furnaces, rail yards, and smelting areas; basaltic glass occurs in volcanic regions.
