mineral

Blue Slag Glass

Anthropogenic Amorphous Silicon Dioxide

Hardness: 5.5-6.5 (Mohs scale), Color: Cobalt blue, Luster: Vitreous, Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.4-2.8

Hardness: 5

Identified June 15, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 (Mohs scale), Color: Cobalt blue, Luster: Vitreous, Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.4-2.8

Formation & geological history

Formed as a byproduct of the iron smelting process, specifically when limestone, iron ore, and fuel are heated together; common in industrial areas from the 19th and early 20th centuries.

Uses & applications

Historically a waste product, but now used for landscaping, decorative gravel, aquarium decor, and vintage jewelry collecting.

Geological facts

Slag glass, also known as 'Leland Blue' in Michigan specifically, is highly sought after by beachcombers despite being a man-made industrial byproduct.

Field identification & locations

Identify by its glass-like bubbles (vesicles), conchoidal (shell-like) fracture patterns, and vibrant colors not typically found in native rocks of the same region.

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