Anthropogenic (Man-made material)
Slag
Metallurgical by-product
Hardness: 5-7 (Mohs scale), Color: Dark grey to black, Luster: Sub-metallic to vitreous (glassy), Structure: Amorphous or microcrystalline, Presence of vesicles (air bubbles), Sharp conchoidal fractures.
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Physical properties
Hardness: 5-7 (Mohs scale), Color: Dark grey to black, Luster: Sub-metallic to vitreous (glassy), Structure: Amorphous or microcrystalline, Presence of vesicles (air bubbles), Sharp conchoidal fractures.
Formation & geological history
Formed as a byproduct of smelting ores (iron, steel, or copper) to separate the metal fraction from the unwanted waste. It is cooled molten rock-like material created in furnaces.
Uses & applications
Used in construction as road base, railroad ballast, roofing granules, and sometimes for producing mineral wool insulation. Often found as industrial waste.
Geological facts
Slag is often mistaken for meteorites due to its dark color, heavy weight, and sometimes magnetic properties, but the presence of vesicles (bubbles) is a primary indicator that it is man-made rather than celestial.
Field identification & locations
Identify by looking for small bubble holes (vesicles) on the surface, a glassy texture on broken edges, and its location near railways, old foundries, or industrial sites. Collectors and geologists use it as an indicator of local human industrial history.
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