Man-made rock-like material
Green Slag Glass
Cullet (Amorphous Silicon Dioxide with impurities)
Hardness: 5-6 (Mohs), Color: Translucent emerald green, Luster: Vitreous, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: ~2.5
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Physical properties
Hardness: 5-6 (Mohs), Color: Translucent emerald green, Luster: Vitreous, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: ~2.5
Formation & geological history
Slag glass is a byproduct of industrial smelting processes or glass manufacturing. It forms as molten residue cools rapidly, creating a glassy texture. The green color often comes from iron, chromium, or copper oxides.
Uses & applications
Primarily used for landscaping, aquarium decor, and decorative garden rock. It is also common in vintage dishware and as a low-cost material for lapidary practice.
Geological facts
While it looks like a mineral such as fluorite or olivine, slag is glass. It is often found near historical iron furnace sites where it was discarded as waste. Identifying features include tiny internal air bubbles and conchoidal (curved) fracture lines.
Field identification & locations
Identify by looking for air bubbles (not found in natural minerals), swirl patterns, and a very smooth, glassy fracture surface. Common locations include old industrial sites, beaches near old ports, and garden centers.
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