Obsidian

Hardness: 5-5.5 (Mohs scale); Color: Black; Luster: Vitreous/Glassy; Structure: Amorphous (Non-crystalline); Cleavage: None, exhibits conchoidal fracture; Specific Gravity: 2.35-2.6

Obsidian is an extrusive igneous rock formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. It is common in areas that have experienced recent volcanic activity.

Historically used for stone tools like arrowheads and knives. Today it is used in jewelry, decorative items, and high-quality surgical scalpel blades because it can be sharpened to a finer edge than steel.

Obsidian edges can reach almost molecular thinness; it is technically a glass, not a mineral, because it lacks a crystalline structure. Ancient civilizations like the Aztecs and Mayans used it for mirrors and weapons.

Identify by its deep black color, glossy surface, and distinctive curved, shell-like (conchoidal) fractures. Found in volcanic regions including Oregon, California, Iceland, and Mexico. Collectors look for unique varieties like Snowflake or Rainbow Obsidian.