Obsidian

Physical Properties

Hardness: 5-5.5 (Mohs scale); Color: Black with potential translucency at edges; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Formation & Geological History

Formed from the rapid cooling of silica-rich (rhyolitic) lava, which prevents crystals from growing. Usually found in geologically young areas with recent volcanic activity (Cenozoic era).

Uses & Applications

Used for making exceptionally sharp surgical blades, high-end jewelry (cabochons), arrowheads/tools, and ornamental decorative stones.

Geological Facts

Obsidian is naturally occurring volcanic glass. Its edges can be thinned down to a molecular level, making it many times sharper than a high-quality steel surgical scalpel. It is technically a 'mineraloid' because it lacks a crystal structure.

Field Identification & Locations

Identify by its characteristic conchoidal (shell-like) fracture, which produces curved ridges as seen in the photograph. It is commonly found in volcanic areas like the Western United States (Oregon, California), Iceland, and Mexico.

Identified on: 4/16/2026

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