mineral

Iron Slag

Anthropogenic Ferro-silicate

Hardness: 5-6 (Mohs); Color: Dark brown/black with reddish oxidation; Luster: Sub-metallic to dull; Structure: Glassy or vesicular (full of holes); Specific Gravity: 3.0-4.0

Hardness: 5-6 (Mohs)
Color: Dark brown/black with reddish oxidation
Luster: Sub-metallic to dull

Identified June 7, 2026More mineral →

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Physical properties

Hardness: 5-6 (Mohs); Color: Dark brown/black with reddish oxidation; Luster: Sub-metallic to dull; Structure: Glassy or vesicular (full of holes); Specific Gravity: 3.0-4.0

Formation & geological history

Formed as a byproduct of smelting iron ore in a blast furnace. While not geological in age, it results from the melting of natural minerals and has a rock-like structure.

Uses & applications

Historical slag was discarded as waste, but modern slag is used as road ballast, in cement manufacturing, and as railroad bed filler.

Geological facts

Slag is often mistaken for meteorites due to its heavy weight, dark color, and melted appearance (pseudo-fusion crust). It represents the history of local industrialization.

Field identification & locations

Look for gas bubbles (vesicles), glassy textures, and proximity to old railway lines or foundries. Identifying by streak (typically black) and lack of nickel helps distinguish from meteorites.