Obsidian

Hardness: 5-5.5 Mohs; Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.6

Formed from the rapid cooling of silica-rich felsic lava. The cooling occurs so quickly that crystals do not have time to grow, resulting in a natural glass. Most specimens are geologically young (less than a few million years) as glass eventually devitrifies.

Historically used for arrowheads and cutting tools; currently used in jewelry, scalpel blades for delicate surgery, and as ornamental decorative stones.

Because it has no crystal structure, obsidian can be fractured to produce an edge that is thinner and sharper than the best steel scalpels. It is also known as 'Dragon glass' in popular culture.

Identify by its curved, razor-sharp conchoidal fracture patterns and intense glassy shine. Found in areas of recent volcanic activity like Oregon, California, Iceland, and Mexico.