Tumbled Obsidian

Physical Properties

Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark brown, Luster: Vitreous/glassy, Crystal structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.35-2.6

Formation & Geological History

Formed from rapidly cooling felsic lava which prevents the formation of crystal structures. Usually found in volcanic regions of various ages, particularly near margins of rhyolitic lava flows.

Uses & Applications

Historically used for blades and arrowheads; currently used in jewelry, ornamental carvings, and specialized surgical blades.

Geological Facts

Obsidian is technically a supercooled liquid because it lacks a crystal structure. It breaks with extremely sharp edges—thinner and sharper than steel scalpels—which is why it is still used in some eye surgeries.

Field Identification & Locations

Identify by its glassy texture, jet black color, and signature conchoidal (shell-like) fracture patterns. Found in places like Oregon, Mexico, and volcanic islands like Iceland.

Identified on: 4/30/2026

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