Obsidian with Spherulitic Devitrification (Snowflake Obsidian/Mahogany related)

Physical Properties

Hardness: 5-5.5 (Mohs scale); Color: Jet black with grey-white or tan patches; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4

Formation & Geological History

Formed from the extremely rapid cooling of felsic (rhyolitic) lava which prevents crystal growth. The light-colored patches are spherulites of cristobalite (a silica polymorph) resulting from devitrification. Most specimens are younger than a few million years as glass eventually devitrifies.

Uses & Applications

Used for making surgical scalpel blades, jewelry, decorative cabochons, and metaphysical collecting. Historically used for arrowheads and scrapers.

Geological Facts

Obsidian fractures into edges that are many times sharper than high-quality steel scalpels. The light-colored 'crust' or patches in this specimen are points where the glass has begun to transform into minerals like quartz or feldspar.

Field Identification & Locations

Identify by its characteristic glassy sheen and sharp conchoidal (shell-like) fracture patterns. Look for it in areas of geologically recent volcanic activity like the American West (Utah, Oregon, California), Iceland, or Mexico.

Identified on: 5/5/2026

Mode: Standard