industrial byproduct

Iron Slag

Anthropogenic pyrometallurgical residue

AI-generated identification · may be incorrect

Hardness (Mohs scale 6-7), dark brown to black color, glassy to metallic luster, amorphous or microcrystalline structure, often contains vesicles (gas bubbles), specific gravity varies depending on iron content.

Identified May 7, 2026More industrial byproduct →

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Physical properties

Formation & geological history

Formed as a byproduct of smelting iron ore in a blast furnace. Modern slag is relatively recent (18th-20th century), occurring when impurities are separated from molten metal.

Uses & applications

Used historically as railroad ballast, in road construction, and as an additive in cement. Rarely used in low-end decorative crafts.

Geological facts

Slag is often mistaken for meteorites due to its dark color, weight, and occasional magnetic properties. It is a record of human industrial history in a specific region.

Field identification & locations

Identify by presence of vesicles (bubbles), flow textures, or a glassy fracture. Often found near old railroads, canal beds, or historical iron mill sites. Use a magnet to check for residual iron.