Anthropgenic (Industrial Byproduct)

Ferrous Slag

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

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.

Other anthropgenic (industrial byproduct) specimens

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Green Glass Slag

Amorphous Silicon Dioxide (SiO2) with metal oxide impurities

mineraloid (man-made)

Slag (Industrial Byproduct)

Artificial silicate/iron byproduct

Mineral description (Anthropogenic material)

Anthropogenic Heat Source (Electronic/Industrial Interface)

Thermal IR emission (Electronic infrastructure)

not a rock or mineral

Slag (Industrial Glassy Byproduct)

Anthropogenic silicate byproduct (Slag)

Mineral-like byproduct (often mistaken for igneous rock or meteorite)

Iron Slag

Anthropogenic Iron Silicate

industrial byproduct

Cobalt Glass Slug (Man-made Glass)

Amorphous Silica with Cobalt Oxide (SiO2 + CoO)

mineraloid