Obsidian

Physical Properties

Hardness: 5-6 (Mohs); Color: Black, dark gray; Luster: Vitreous; Crystal Structure: Amorphous; Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.

Formation & Geological History

Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in areas with recent volcanic activity (Cenozoic era).

Uses & Applications

Used historically for surgical scalpels and arrowheads due to its sharp edges; used today in jewelry, decorative items, and specialized scalpels.

Geological Facts

Obsidian can produce a cutting edge many times sharper than high-quality steel surgical scalpels. It is technically a mineraloid because it lacks a crystal structure.

Field Identification & Locations

Identify by its smooth, glassy texture and distinctive shell-like (conchoidal) fracture patterns. Found in volcanic regions like Iceland, Mexico, and the Western USA.

Identified on: 5/1/2026

Mode: Standard