Mineraloid (Industrial byproduct)

Slag (Industrial Glass Slag)

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

Hardness: 5-6 (Mohs); Color: Olive green to brownish with glassy spheres; Luster: Vitreous to dull; Structure: Amorphous (non-crystalline); Specific Gravity: 2.5-4.0

Hardness: 5-6 (Mohs)
Color: Olive green to brownish with glassy spheres
Luster: Vitreous to dull

Identified April 19, 2026More mineraloid (industrial byproduct) →

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Physical properties

Hardness: 5-6 (Mohs); Color: Olive green to brownish with glassy spheres; Luster: Vitreous to dull; Structure: Amorphous (non-crystalline); Specific Gravity: 2.5-4.0

Formation & geological history

Formed as a byproduct of the smelting process when purifying metals like iron or copper. Impurities (gangue) fuse together with flux materials at high temperatures and cool quickly, forming a glassy waste material.

Uses & applications

Used as railroad ballast, road base material, abrasive grit for sandblasting, and occasionally for glass manufacturing or decorative landscaping.

Geological facts

Slag can often look like volcanic rocks or meteorites due to gas bubbles (vesicles), but its glassy texture and unusual colors usually indicate industrial origin. It is commonly found near old steel mills or historical foundry sites.

Field identification & locations

Identify by looking for spherical gas bubbles (vesicles), a glassy/shell-like fracture (conchoidal), and unexpected colors like bright blue, green, or purple. Often found along old railroad tracks and riverbeds near industrial zones.

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Green Slag Glass

Amorphous Silica / Glassy Blast Furnace Slag

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Cullet Glass (sometimes mistaken for Blue Obsidian or Slag)

Amorphous Silicon Dioxide (SiO2) with chemical additives (e.g., Cobalt for blue color)

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Red Slag Glass

Amorphous Silica (Industrial byproduct with metallic oxide dopants)

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Green Slag

Anthropogenic Silicate Glass

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Slag (Industrial Glass/Metal Waste)

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Cobalt Glass Slug (Man-made Glass)

Amorphous Silica with Cobalt Oxide (SiO2 + CoO)

mineraloid