Obsidian

Physical Properties

Hardness: 5-5.5 (Mohs); Color: jet black, dark gray/brown; Luster: vitreous (glassy); Crystal structure: amorphous (none); Cleavage: none, shows conchoidal fracture; Specific gravity: 2.35-2.6.

Formation & Geological History

Formed from extrusive volcanic active; specifically when highly viscous, silica-rich lava cools extremely rapidly, preventing internal crystal growth. Found in geologically recent volcanic fields.

Uses & Applications

Used in surgical scalpel blades for precision, jewelry (pendants, beads), landscaping, and high-end mirrors. Historically used for arrowheads and scrapers.

Geological Facts

Obsidain is technically a glass rather than a mineral because it lacks a crystalline structure. Ancient Aztecs used obsidian mirrors for divination, associating it with the god Tezcatlipoca.

Field Identification & Locations

Identify by its glass-like texture and sharp, curved (conchoidal) edges when broken. Commonly found in locations like Glass Buttes (Oregon), Yellowstone, or volcanic regions in Mexico and Iceland.

Identified on: 5/6/2026

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