igneous
Obsidian
Volcanic Glass (SiO2 + impurities)
Hardness: 5-6 (Mohs); Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.3-2.6
- Hardness
- 5-6 (Mohs)
- Color
- Jet black
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-6 (Mohs); Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.3-2.6
Formation & geological history
Formed through the rapid cooling of silica-rich (rhyolitic) lava, preventing crystal growth. It is found in geologically recent volcanic fields or areas with Cenozoic volcanic activity.
Uses & applications
Used for making jewelry, polished stones, surgical scalpel blades (due to its ability to hold an edge thinner than steel), and ornamental items.
Geological facts
Obsidian was highly prized by ancient civilizations, including the Aztecs and Mayans, for making weapons and cutting tools. It is not technically a mineral because it lacks a crystal structure.
Field identification & locations
Identify by its glassy surface and distinct curved, shell-like (conchoidal) fractures. Found in volcanic regions such as the American West (Oregon, California, Iceland, and Mexico.
