mineral-like (anthropogenic)
Slag (Industrial By-product)
Glassy silicate or metallic smelting residue
Hardness: 5-7 (variable). Color: Dark gray, brown, to black. Luster: Vitreous to dull/metallic. Crystal Structure: Amorphous (glassy). Cleavage: None (conchoidal fracture). Specific Gravity: High to very high if iron-rich. High porosity with vesicles (gas bubbles).
- Hardness
- 5-7 (variable)
- Color
- Dark gray, brown, to black
- Luster
- Vitreous to dull/metallic
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Physical properties
Hardness: 5-7 (variable). Color: Dark gray, brown, to black. Luster: Vitreous to dull/metallic. Crystal Structure: Amorphous (glassy). Cleavage: None (conchoidal fracture). Specific Gravity: High to very high if iron-rich. High porosity with vesicles (gas bubbles).
Formation & geological history
Slag is the glass-like by-product left over after a desired metal has been separated from its raw ore during the smelting process. It is often found near historical ironworks, steel mills, or railroads. It is not a natural rock but a byproduct of human industry.
Uses & applications
Historical slag is primarily of interest to collectors or as a decorative aggregate. Industrially, modern slag is used in cement manufacturing, road base construction, and as railroad ballast.
Geological facts
Slag is often mistaken for meteorites due to its dark color, heavy weight, and occasional metallic sheen. However, the presence of vesicles (gas bubble holes) is a definitive sign that it is not a meteorite.
Field identification & locations
Identify in the field by looking for 'swiss cheese' bubbles (vesicles), a glassy or metallic texture, and a high density. It is often found in areas with a history of iron production or near old railway tracks where it was used as ballast.
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