Obsidian

Physical Properties

Hardness: 5–5.5; Color: Deep black to dark brown; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Formation & Geological History

Formed from rapid cooling of felsic lava, which prevents the growth of crystals. Typically found in volcanic regions of various ages, from the Cenozoic era to recent.

Uses & Applications

Historically used for cutting tools and arrowheads; currently used in scalpels for surgery, jewelry, ornamental carvings, and gemstone collecting.

Geological Facts

Obsidian can be sharper than high-quality steel scalpels. It is technically a 'mineraloid' rather than a mineral because it lacks a crystalline structure.

Field Identification & Locations

Identify by its characteristic shell-like (conchoidal) fracture and sharp edges. Commonly found in places with recent volcanic activity like the western USA, Mexico, and Iceland.

Identified on: 4/26/2026

Mode: Standard