Antropogenic (Man-made material)
Red Slag Glass (Cullet)
Amorphous Silicon Dioxide (SiO2) with metallic dopants
Hardness: 5.5-6 (Mohs scale); Color: Vibrant translucent to opaque red; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: None, exhibits shell-like conchoidal fracture; Specific gravity: approx. 2.4-2.8
- Hardness
- 5
- Color
- Vibrant translucent to opaque red
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5.5-6 (Mohs scale); Color: Vibrant translucent to opaque red; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: None, exhibits shell-like conchoidal fracture; Specific gravity: approx. 2.4-2.8
Formation & geological history
Formed as a byproduct of industrial glass manufacturing or iron smelting processes. It is produced when molten remains of silica cooling too quickly for atoms to arrange into a crystal lattice. Most specimens date from the mid-19th to 20th century.
Uses & applications
Commonly used as decorative garden stones, fish tank gravel, lapidary training material, or as 'rough' for costume jewelry and artisanal glass art.
Geological facts
While it can be mistaken for rare volcanic obsidian or giant gemstones like garnet or ruby, the presence of internal bubbles (gas vesicles) and the absence of a crystal structure confirm its industrial origin. Deep red glass is often colored using gold or selenium.
Field identification & locations
Identify in the field by looking for air bubbles, swirl patterns (flow lines), and sharp conchoidal edges. Found primarily near historic glass factory sites or industrial dump regions in the Rust Belt of the USA and parts of Western Europe.
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