Obsidian

Physical Properties

Hardness: 5-5.5 on Mohs scale. Color: Black to dark grey. Luster: Vitreous/glassy. Crystal Structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.4.

Formation & Geological History

Formed through the rapid cooling of silica-rich lava (rhyolitic) which prevents crystal growth. Usually found in geologically young volcanic regions (Quaternary period).

Uses & Applications

Historically used for arrowheads and cutting tools. Today used in scalpel blades, jewelry, and as decorative gemstones.

Geological Facts

Because it is glass and lacks a crystal structure, its edges can be thinned down to nearly molecular thickness, making it sharper than even the finest steel surgical scalpels.

Field Identification & Locations

Identify by its glass-like appearance and conchoidal (shell-like) fracture patterns. Frequently found in volcanic fields such as those in the Western United States, Mexico, and Iceland.

Identified on: 5/7/2026

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