Mineral byproduct (Anthropogenic)
Ferro-silicate Slag
Industrial Vitrified Slag (High-silica amorphous glass)
Hardness: 5.5-6.5 (Mohs), Color: Dark grey/blue-grey with glass-like pockets, Luster: Vitreous to dull, Structure: Amorphous (non-crystalline), Cleavage: Conchoidal (shell-like fractures), Specific Gravity: 2.5-3.5.
- Hardness
- 5
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Physical properties
Hardness: 5.5-6.5 (Mohs), Color: Dark grey/blue-grey with glass-like pockets, Luster: Vitreous to dull, Structure: Amorphous (non-crystalline), Cleavage: Conchoidal (shell-like fractures), Specific Gravity: 2.5-3.5.
Formation & geological history
Formed as an industrial byproduct of iron or steel smelting. The glass-like sections form when molten silicate waste cools rapidly. The bubbles (vesicles) are trapped gas pods from the smelting process. Date: Likely 19th or 20th century.
Uses & applications
Historical use as road base, railroad ballast, or fill material. Occasionally used in 'slag jewelry' or as landscape decorative stone.
Geological facts
Slag is often mistaken for meteorites due to its weight and unusual textures, but the presence of circular gas bubbles (vesicles) and glass-like fractures identify it as man-made. It is frequently found near historical ironworks or riverbeds used for industrial disposal.
Field identification & locations
Identify by looking for air bubbles, sharp glass-like edges, and a lack of clear Earth-layering. Often found in areas with past industrial activity or on old farmsteads where it was used for construction foundations.
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