mineraloid
Cobalt Glass Slug (Man-made Glass)
Amorphous Silica with Cobalt Oxide (SiO2 + CoO)
Hardness: 5.5-6.0; Color: Vibrant cobalt blue; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.4-2.8
- Hardness
- 5
- Color
- Vibrant cobalt blue
- Luster
- Vitreous (glassy)
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Physical properties
Hardness: 5.5-6.0; Color: Vibrant cobalt blue; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.4-2.8
Formation & geological history
Synthetic/Industrial byproduct. Formed by melting silica sand with flux and adding cobalt oxide as a pigment. This is not a naturally occurring mineral but a piece of industrial glass cullet or a decorative glass fragment.
Uses & applications
Primarily used for decorative landscaping, jewelry making, aquarium decor, and stained glass production.
Geological facts
Cobalt is such a powerful coloring agent that as little as 0.1% of it can turn glass a deep, royal blue. Before the modern era, similar blue glass was often referred to as 'smalt' and used as a permanent blue pigment in oil paintings.
Field identification & locations
Identify in the field by its distinct conchoidal (curved/shell-like) fracture, intense uniform blue color, and presence of tiny air bubbles or 'seeds' trapped inside the glass. Commonly found at industrial sites or sold as decorative stones.
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