Anthropogenic (Man-made)

Slag (Anthropogenic Glass/Iron byproduct)

Ferro-silicate Slag

Hardness: 5-7 Mohs; Color: Black, dark grey, or brownish with occasional iridescent sheen; Luster: Glassy to metallic; Structure: Amorphous/Vesicular (contains air bubbles/gas pockets); Specific Gravity: Varries (2.5 - 4.0).

Hardness: 5-7 Mohs
Luster: Glassy to metallic

Identified March 15, 2026More anthropogenic (man-made) →

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Physical properties

Formation & geological history

Formed as a byproduct of smelting ores (iron, copper, etc.) or glass manufacturing. During the cooling process, impurities rise to the top and solidify. Most surface specimens date from the Industrial Revolution (18th-20th century).

Uses & applications

Historically used for road ballast, railroad fill, and occasionally as an additive in cement. Rarely used as a decorative 'stone' in landscaping or folk art.

Geological facts

Slag is the most common 'meteorite-wrong'—specimens mistaken for meteorites. Unlike real meteorites, slag frequently contains vesicles (holes from gas bubbles) which do not occur in stone or iron meteorites.

Field identification & locations

Identify by looking for glass-like fractures (conchoidal), internal air bubbles, and flow textures. Found globally near old blast furnaces, railroads, and industrial sites. It is often magnetic if iron-rich.

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Mineral equivalent / Metal Alloy

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Ferruginous Conglomerate (or Iron-Rich Concrete/Slag)

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sedimentary

Concrete Rubble with Aggregate

Hardened Portland Cement Paste with Coarse Aggregate

Anthropogenic (Man-made)