Mineraloid (Industrial byproduct)

Green Slag Glass

Amorphous Silica / Glassy Blast Furnace Slag

Hardness: 5.5-6 (Mohs); Color: Emerald green with translucent iridescence; Luster: Vitreous to pearly; Crystal structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.4-2.8

Hardness: 5
Color: Emerald green with translucent iridescence
Luster: Vitreous to pearly

Identified April 7, 2026More mineraloid (industrial byproduct) →

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Physical properties

Formation & geological history

Formed as a byproduct of smelting ores (such as iron or copper) or glass manufacturing. When the molten silica cools rapidly, it solidifies into a glass rather than crystallizing. Many specimens found today date back to the late 19th and early 20th centuries.

Uses & applications

Commonly used in landscaping, decorative stone gardens, aquarium decor, and sometimes wire-wrapped jewelry or lapidary art for 'metaphysical' purposes.

Geological facts

Slag glass is often mistaken for obsidian or precious minerals like emerald or fluorite. Because it is a human-made byproduct, it frequently contains tiny air bubbles or swirl patterns not typically found in natural stones.

Field identification & locations

Identify in the field by looking for conchoidal (shell-shaped) fractures, air bubbles, and extremely vibrant colors that look 'too perfect'. Often found near historic industrial sites, railroads, or shoreline dumping grounds.

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Cullet Glass (sometimes mistaken for Blue Obsidian or Slag)

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Amorphous Silicate Glass (often containing Al, Ca, Mg, and Ti oxides)

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Green Slag

Anthropogenic Silicate Glass

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Slag (Industrial Glass/Metal Waste)

Artificial silicate/ferro-silicate byproduct

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Cullet Glass (Slag Glass)

Amorphous Silicon Dioxide (Industrial Byproduct)

mineraloid