mineral
Slag Glass (Leland Blue variant)
Anthropogenic Vitreous Silicate
Hardness: 5.5-6 (Mohs); Color: Pale mint green with air bubbles (vacuoles) and dark inclusions; Luster: Vitreous to dull; Crystal structure: Amorphous; Cleavage: Conchoidal.
- Hardness
- 5
- Luster
- Vitreous to dull
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Physical properties
Hardness: 5.5-6 (Mohs); Color: Pale mint green with air bubbles (vacuoles) and dark inclusions; Luster: Vitreous to dull; Crystal structure: Amorphous; Cleavage: Conchoidal.
Formation & geological history
Slag is a byproduct of the iron ore smelting process. Historically, in the late 19th century, impurities separated from molten iron formed a glassy scum that was dumped into bodies of water (like Lake Michigan) to cool. Over decades, water erosion tumbled these pieces into smooth, stone-like specimens.
Uses & applications
Used primarily in lapidary work, artisan jewelry (pendants and rings), and as a collectible beach find.
Geological facts
While technically a man-made byproduct, it is treated as a gemstone in Michigan. Green variants are less common than blue ones but are part of the same historical iron-smelting legacy. The air bubbles are a key distinguishing feature from natural agate or turquoise.
Field identification & locations
Identify by looking for the tell-tale 'bubbles' or pits on the surface and a glassy, conchoidal fracture on broken edges. Commonly found on the shores of Lake Michigan, particularly near Leland and Elk Rapids.
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