Obsidian

Physical Properties

Hardness: 5-6 (Mohs); Color: Black, deep brown, or grey; Luster: Vitreous/glassy; Crystal structure: Amorphous; Cleavage: None (conchoidal fracture); Specific gravity: 2.35-2.6

Formation & Geological History

Formed from rapid cooling of felsic lava, preventing crystal growth. It is typically found in tertiary or quaternary volcanic regions globally.

Uses & Applications

Used in ornamental jewelry, scalpel blades for high-precision surgery, decorative items, and historical weapon/tool making.

Geological Facts

Obsidian has been used since prehistoric times for sharp tools. Some of the sharpest blades in existence are made of obsidian, with an edge only molecules thick.

Field Identification & Locations

Identify by its characteristic conchoidal (shell-like) fracture and sharp edges. Common in areas of recent volcanic activity like the American West, Iceland, and Mexico.

Identified on: 5/2/2026

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