Obsidian

Physical Properties

Hardness: 5-6 (Mohs scale), Color: Jet black to dark grey, Luster: Vitreous (glassy), Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6

Formation & Geological History

Formed from rapid cooling of felic (silica-rich) lava, preventing crystal growth. Usually found in geologically young volcanic areas (Cenozoic or later) because glass devitrifies over time.

Uses & Applications

Historical use for sharp tools and weapons (scalpels, arrowheads); modern use in jewelry, home decor, and high-precision surgical blades.

Geological Facts

Obsidian is often called 'nature's glass'. It can produce an edge that is many times sharper than a steel scalpel because it breaks at a molecular level.

Field Identification & Locations

Identify by its glass-like texture and characteristic shell-like (conchoidal) fractures. Found in volcanic regions like the American West (Glass Buttes), Iceland, and Italy (Lipari). Watch for sharp edges when handling.

Identified on: 4/19/2026

Mode: Standard