Obsidian

Physical Properties

Hardness: 5–5.5 Mohs scale; Color: Black to deep brown (wet look); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None; Fracture: Conchoidal (displays smooth, curved surfaces).

Formation & Geological History

Formed through the rapid cooling of silica-rich felsic lava, which prevents crystal growth. It is found in geologically recent volcanic areas (usually less than a few million years old) due to its tendency to devitrify over time.

Uses & Applications

Used historically for sharp tools and weapons (arrowheads/knives); currently used for surgical scalpel blades, jewelry, decorative gemstones, and Feng Shui ornaments.

Geological Facts

Obsidian breaks into edges that are thinner and sharper than a high-quality steel scalpel, even down to a single molecule thick. It has been traded across continents by ancient civilizations for over 10,000 years.

Field Identification & Locations

Identify by its 'shell-like' conchoidal fractures and sharp edges. In the field, look for glassy, translucent edges when held to the light. Common in volcanic regions like the American West (Iceland, Mexico, Oregon).

Identified on: 4/20/2026

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