Anthropgenic (Industrial Byproduct)

Ferrous Slag

Iron/Steel Slag (Complex Calcium-Alumino-Silicates)

AI-generated identification · may be incorrect

Hardness: 5-7 (Mohs); Color: Dark grey to black with metallic or glassy sheen; Luster: Vitreous to sub-metallic; Structure: Amorphous/vughy; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-4.0

Hardness: 5-7 (Mohs)
Color: Dark grey to black with metallic or glassy sheen
Luster: Vitreous to sub-metallic

Identified March 20, 2026More anthropgenic (industrial byproduct) →

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Physical properties

Formation & geological history

Formed during the smelting of iron ore in a blast furnace. It is a glass-like byproduct that separates from the molten metal. Found in industrial areas, historic rail beds, and abandoned mining or smelting sites.

Uses & applications

Used widely in construction as road base, railroad ballast, raw material for cement, and occasionally as an abrasive for sandblasting.

Geological facts

Slag is often mistaken for meteorites (meteorites are generally not vesicular/bubbly) or obsidian. While man-made, ancient Roman slag piles are now studied by archaeologists to understand early metallurgy.

Field identification & locations

Identify by looking for 'vesicles' (gas bubbles), a glassy/slaggy texture, and often a higher density than common rocks. Frequently found near old railroad tracks or historic industrial centers.