not a natural rock

Man-made Slag (Industrial Byproduct)

Anthropogenic Glassy Residue

Hardness: 5.5-6.5 (Mohs scale); Color: Black, dark gray, or multi-colored; Luster: Vitreous to dull; Structure: Amorphous/Glassy; Cleavage: Conchoidal fracture; Specific Gravity: 2.5-4.0 (highly variable)

Hardness: 5
Color: Black, dark gray, or multi-colored
Luster: Vitreous to dull

Identified March 22, 2026More not a natural rock →

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Physical properties

Formation & geological history

Formed as a byproduct of smelting ores (iron, steel, copper) where impurities are separated from molten metal. This specimen appears to be modern industrial waste rather than a natural geological formation.

Uses & applications

Used in construction as road base, railroad ballast, or aggregate in concrete. Occasionally used in the production of mineral wool insulation.

Geological facts

Slag can often be mistaken for obsidian or meteorites, but the presence of vesicles (gas bubbles) or bits of embedded metal often distinguishes it as industrial in origin.

Field identification & locations

Commonly found near historical smelting sites, railroads, or landfills. Identified by its weight, glassy texture, and lack of natural crystalline structure typical of minerals.

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