Antropogenic (Man-made industrial byproduct)
Ferrosilicon Slag (Industrial Vitrified Glass)
Vitreous Silicate Residue
Hardness: 5.5-6.5 (Mohs); Color: Dark teal, blue-green, or brownish; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.5-4.0 depending on metal content.
- Hardness
- 5
- Color
- Dark teal, blue-green, or brownish
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5.5-6.5 (Mohs); Color: Dark teal, blue-green, or brownish; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.5-4.0 depending on metal content.
Formation & geological history
Formed as a byproduct of smelting processes, specifically the production of ferrosilicon or other metal alloys. It is created when molten silicates cool rapidly, forming a glass-like substance. It is essentially modern industrial 'obsidian'.
Uses & applications
Used primarily as road ballast, construction aggregate, or abrasive grit. Occasionally used by lapidary hobbyists for tumbling or carving due to its unique swirls and colors.
Geological facts
Slag is often mistaken for rare gemstones like emerald or obsidian. It frequently contains small trapped gas bubbles (vesicles), which are a key indicator of its industrial origin rather than a natural geological formation.
Field identification & locations
Identify in the field by the presence of conchoidal fractures, swirl patterns in the color, and the presence of bubbles. Commonly found near old railroad beds, historic iron forges, or modern smelting facilities.
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