Obsidian

Physical Properties

Hardness: 5-5.5 (Mohs), Color: Black, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (none), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6

Formation & Geological History

Formed through the rapid cooling of silica-rich (felsic) lava, which prevents crystal growth. It is typically found in geologically young volcanic regions (Tertiary to Quaternary age).

Uses & Applications

Used in ornamental jewelry, scalpel blades for high-precision surgery, and as a sought-after specimen for rock collectors.

Geological Facts

Obsidian fractures with extremely sharp edges, which is why it was used to create arrowheads and knives across ancient cultures; it is actually a liquid that cooled so fast it became a solid without crystallizing.

Field Identification & Locations

Identify by its glass-like texture, deep black color, and distinctive curved, shell-like (conchoidal) fracture lines. Commonly found in volcanic areas like the American West (Glass Buttes, Oregon), Iceland, and Mexico.

Identified on: 5/5/2026

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