igneous
Obsidian
Volcanic Glass (High silica amorphous rock)
Hardness: 5-6 (Mohs); Color: Black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; SG: 2.35-2.6
- Hardness
- 5-6 (Mohs)
- Color
- Black
- Luster
- Vitreous/Glassy
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Physical properties
Hardness: 5-6 (Mohs); Color: Black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; SG: 2.35-2.6
Formation & geological history
Formed through the rapid cooling of felsic (silica-rich) lava. It cools so quickly that crystals do not have time to grow, resulting in a volcanic glass appearance.
Uses & applications
Historically used for making sharp tools and weapons (arrowheads, blades). Today used in jewelry, ornamental sculptures, and high-end surgical scalpel blades.
Geological facts
Obsidian fractures with extremely sharp edges, often thinner and sharper than a steel scalpel. Types include snowflake, mahogany, and rainbow obsidian.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture patterns and glassy texture. Commonly found in volcanic regions like the American West (Glass Buttes), Iceland, and Mexico.
