Anthropogenic/Industrial byproduct
Ferrous Slag
Fused calcium-iron silicates (Industrial Slag)
Variable hardness (5-7 Mohs), dark grey to black color, vitreous to metallic luster, amorphous or microcrystalline structure, vesicular (pitted with gas bubbles), high density if iron-rich.
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Physical properties
Variable hardness (5-7 Mohs), dark grey to black color, vitreous to metallic luster, amorphous or microcrystalline structure, vesicular (pitted with gas bubbles), high density if iron-rich.
Formation & geological history
Formed as a byproduct of the smelting process in iron and steel manufacturing. It consists of the glass-like silicates and impurities separated from molten metal. Age is typically modern (industrial era).
Uses & applications
Used in road construction, as an ingredient in cement/concrete, as railroad ballast, or as an abrasive blasting medium.
Geological facts
Slag is often mistaken for meteorites because of its weight and dark, melted-looking surface. However, the presence of vesicles (bubbles) is a primary indicator of artificial smelting or volcanic origin, whereas meteorites almost never contain bubbles.
Field identification & locations
Identify in the field by looking for 'glassy' textures mixed with metallic or dull grey surfaces, and distinctive circular gas bubbles (vesicles). Found commonly near historic steel mills, old railway beds, or industrial dump sites.
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