igneous
Obsidian (Blue)
Volcanic Glass (SiO2)
Hardness: 5-5.5; Color: Deep blue to translucent cobalt; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None/Conchoidal fracture; Specific gravity: 2.35-2.6
- Hardness
- 5-5
- Color
- Deep blue to translucent cobalt
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-5.5; Color: Deep blue to translucent cobalt; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None/Conchoidal fracture; Specific gravity: 2.35-2.6
Formation & geological history
Formed by the rapid cooling of silica-rich lava which prevents crystallization. Blue varieties are often created when trace elements or gas bubbles interact with the light, though many deep blue specimens on the market are human-processed cobalt glass.
Uses & applications
Used for making jewelry, decorative spheres, ornamental carvings, and in some surgical applications for scalpel blades due to its extreme sharpness when fractured.
Geological facts
Obsidian was highly prized by ancient civilizations for stone tools and weapons. Natural blue obsidian is extremely rare; most bright blue spheres available commercially are actually man-made cobalt glass.
Field identification & locations
Identify by its smooth, glassy texture and conchoidal (shell-like) fractures. Collectors check for natural inclusions to distinguish from manufactured glass.
