igneous
Obsidian
Amorphous volcanic glass (principally SiO2)
Hardness: 5-5.5 | Color: Jet black to dark brown/green | Luster: Vitreous/Glassy | Structure: Amorphous (non-crystalline) | Fracture: Conchoidal | Specific Gravity: 2.4
- Hardness
- 5-5
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Physical properties
Hardness: 5-5.5 | Color: Jet black to dark brown/green | Luster: Vitreous/Glassy | Structure: Amorphous (non-crystalline) | Fracture: Conchoidal | Specific Gravity: 2.4
Formation & geological history
Formed from the rapid cooling of felsic lava, preventing crystal growth. It occurs in areas of geologically recent volcanic activity, typically dating from the Cenozoic era.
Uses & applications
Used historically for surgical blades, arrowheads, and tools. Currently used for gemstone jewelry, ornamental carvings, and high-end surgical scalpels.
Geological facts
Obsidian is technically not a mineral because it is a glass and lacks a crystalline structure. It is extremely sharp, with an edge that can be much thinner than even a diamond-edged scalpel.
Field identification & locations
Identify in the field by its distinct glassy luster and shell-like (conchoidal) fracture patterns when broken. Common in the Western US, Mexico, and Greece.
