industrial byproduct (anthropogenic)
Iron Slag
Anthropogenic Vitreous Ferrous Silicate
Hardness: 5-7 (Mohs). Color: Dark gray to black, often with rusty oxidation. Luster: Metallic to glassy. Structure: Amorphous/Vesicular (bubbly/porous). Cleavage: None, often conchoidal fracture. Specific Gravity: Variable (3.0–3.8).
- Hardness
- 5-7 (Mohs)
- Color
- Dark gray to black, often with rusty oxidation
- Luster
- Metallic to glassy
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Physical properties
Hardness: 5-7 (Mohs). Color: Dark gray to black, often with rusty oxidation. Luster: Metallic to glassy. Structure: Amorphous/Vesicular (bubbly/porous). Cleavage: None, often conchoidal fracture. Specific Gravity: Variable (3.0–3.8).
Formation & geological history
Formed as a byproduct of smelting ores (iron or copper). The process involves heating metal ores to separate pure metal from waste; the cooled molten waste forms slag. These can range from modern to centuries old.
Uses & applications
Used as road ballast, railroad track bedding, abrasive grit, and occasionally as an inexpensive aggregate in concrete or landscaping.
Geological facts
Often mistaken for meteorites due to their heavy weight and unusual 'melted' appearance. However, the presence of bubbles (vesicles) is a definitive indicator of slag or terrestrial volcanic rock, as true meteorites lack bubbles.
Field identification & locations
Identify by looking for spherical gas bubbles, flow textures, and lack of internal metallic flecks (chondrules) seen in meteorites. Often found near old railroads, canal banks, and historical industrial sites.
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