igneous (anthropogenic)
Slag (Industrial Glass/Byproduct)
Anthropogenic Vitreous Silicate
Hardness: 5.5-6.5 (Mohs scale); Color: Dark grey, brownish, or metallic; Luster: Glassy to dull; Crystal structure: Amorphous/Vitreous; Cleavage: None/Conchoidal fracture; Contains vesicles (gas bubbles).
- Hardness
- 5
- Color
- Dark grey, brownish, or metallic
- Luster
- Glassy to dull
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Physical properties
Hardness: 5.5-6.5 (Mohs scale); Color: Dark grey, brownish, or metallic; Luster: Glassy to dull; Crystal structure: Amorphous/Vitreous; Cleavage: None/Conchoidal fracture; Contains vesicles (gas bubbles).
Formation & geological history
Formed as a byproduct of smelting ores (like iron, copper, or lead) where impurities are separated from the metal. Molten slag cools rapidly on the surface or in piles, creating a glass-like or stony texture. These can date from the Industrial Revolution to modern times.
Uses & applications
Historically used for road ballast, railroad beds, and occasionally as an aggregate in concrete. It is also a popular 'curiosity' item for amateur rockhounds who misidentify it as meteorites.
Geological facts
Slag is often the most common 'meteor-wrong' found by collectors because of its metallic appearance, heavy weight, and presence of gas bubbles (vesicles), which real meteorites almost never have.
Field identification & locations
Identify by looking for spherical gas bubbles (vesicles), a glassy texture upon breaking, and flow lines on the surface. It is commonly found near old railways, industrial sites, or historic furnace locations.
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