Obsidian

Physical Properties

Hardness: 5-5.5 (Mohs scale); Color: Black, dark brown, or grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Formation & Geological History

Formed from the rapid cooling of silica-rich (rhyolitic) lava, preventing crystal growth. Usually found in volcanic regions from the Cenozoic era or younger, as glass devitrifies over millions of years.

Uses & Applications

Historically used for arrowheads and knives; currently used as a gemstone in jewelry, as surgical scalpel blades for cleaner cuts, and as a decorative stone.

Geological Facts

Obsidian is actually a liquid that has cooled so quickly it became a solid without crystallizing. Some varieties like Snowflake Obsidian contain white radially clustered crystals of cristobalite.

Field Identification & Locations

Identify by its glass-like texture and sharp, curved (conchoidal) edges. Found in the Western US (Oregon, California), Iceland, Japan, and Mexico. Use caution when handling as edges can be sharper than steel.

Identified on: 4/19/2026

Mode: Standard