Synthetic/Byproduct (Non-igneous, non-sedimentary, non-metamorphic)
Green Slag Glass (Cullet)
Amorphous Silica (Industrial Glass Byproduct)
Hardness: 5.5-6 (Mohs scale); Color: Vibrant emerald to forest green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4-2.8
- Hardness
- 5
- Color
- Vibrant emerald to forest green
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5.5-6 (Mohs scale); Color: Vibrant emerald to forest green; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4-2.8
Formation & geological history
Formed as a byproduct of historical iron smelting or glass manufacturing processes. Raw silica and impurities are superheated into a molten state and then cooled rapidly, preventing crystal formation. Most specimens found today date from the mid-19th to early 20th centuries.
Uses & applications
Primary modern uses include landscaping (fire pits and rock gardens), aquarium decor, glass recycled for terrazzo flooring, and 'fake emerald' jewelry for craft purposes.
Geological facts
Many hobbyists often mistake green slag for obsidian or raw emerald. It is a 'technofossil' that provides evidence of historical industrial activity in specific regions like the Rust Belt of the United States.
Field identification & locations
Identify in the field by looking for gas bubbles (voids), conchoidal fracture patterns with sharp edges, and a lack of organized crystal faces. Common in historical industrial areas near riverbeds or old foundry sites.
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