Black Obsidian

Physical Properties

Hardness: 5-5.5 (Mohs); Color: Jet black to dark grey; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4

Formation & Geological History

Formed through the rapid cooling of silica-rich (felsic) lava, preventing the formation of crystals. It is found in volcanic regions from various geological ages, primarily the Cenozoic era.

Uses & Applications

Used for making scalpel blades in modern surgery, ornamental jewelry, carvings, and historically for arrowheads and cutting tools.

Geological Facts

Obsidian fractures with a conchoidal break, creating edges that are sharper than even the highest quality steel scalpels. It is not a true mineral because it lacks a crystal structure.

Field Identification & Locations

Identify in the field by its glassy texture, shell-like (conchoidal) fractures, and sharp edges. Commonly found in California, Mexico, Iceland, and Italy near volcanic sites.

Identified on: 4/28/2026

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