Antropogenic rock (Man-made)
Slag (Industrial Glass/Metal)
Ferrous slag or Glassy silicate byproduct
Hardness: 5-6 (Mohs); Color: Dark brown to black with a metallic sheen; Luster: Vitreous to sub-metallic; Structure: Amorphous/Vesicular; Cleavage: None (conchoidal fracture); Specific Gravity: Varries (2.5-3.5)
- Hardness
- 5-6 (Mohs)
- Color
- Dark brown to black with a metallic sheen
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark brown to black with a metallic sheen; Luster: Vitreous to sub-metallic; Structure: Amorphous/Vesicular; Cleavage: None (conchoidal fracture); Specific Gravity: Varries (2.5-3.5)
Formation & geological history
Formed as a byproduct of smelting ores (iron, steel, or copper) or glass manufacturing where gas bubbles expand and escape from a cooling molten liquid, creating a 'vesicular' or hole-filled texture.
Uses & applications
Historically used as railroad ballast, road base material, or concrete aggregate. Occasionally used in jewelry as 'Leland Blue' or 'Detroit Agate' if colorful, otherwise a common collector curiosity.
Geological facts
Slag is often mistaken for meteorites due to its dark color, metallic appearance, and weight. However, true meteorites almost never contain vesicles (gas bubbles), which are a hallmark of slag or volcanic rock.
Field identification & locations
Identify by looking for spherical gas bubbles (vesicles), glass-like edges, and flow patterns. Commonly found near historical industrial sites, railroads, or riverbeds near former mills.
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