Anthropogenic (Man-made)

Slag Glass (Cullet)

Amorphous Silicon Dioxide (SiO2) with metal oxide colorants

Hardness: 5.5-6 (Mohs scale); Color: Vibrant turquoise or aqua; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4-2.8

Hardness: 5
Color: Vibrant turquoise or aqua
Luster: Vitreous (glassy)

Identified March 26, 2026More anthropogenic (man-made) →

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Physical properties

Hardness: 5.5-6 (Mohs scale); Color: Vibrant turquoise or aqua; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4-2.8

Formation & geological history

Formed as a byproduct of industrial glass manufacturing or metal smelting. This specific turquoise specimen is 'cullet' or waste glass that has cooled slowly into large chunks. It lacks a geological age as it is modern.

Uses & applications

Used primarily for landscaping, decorative garden features, aquarium decor, and sometimes lapidary work (cabbing) for costume jewelry.

Geological facts

While often mistaken for volcanic obsidian or high-grade minerals like turquoise or beryl, slag glass is easily identified by the presence of small internal gas bubbles and its distinct 'wavy' flow lines.

Field identification & locations

Identify in the field by looking for air bubbles, lack of crystal structure, and extreme conchoidal (shell-like) fractures. It is frequently found near historical iron furnace sites or glass factories.

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