Obsidian

Hardness 5-5.5, jet black to dark brown color, vitreous luster, amorphous crystal structure, conchoidal fracture, specific gravity 2.35-2.45.

Formed from rapidly cooled felsic lava extruded from a volcano, preventing crystal growth. Found globally in regions with recent volcanic activity.

Used historically for sharp cutting tools and arrowheads, and presently in ornamental jewelry, decorative objects, and occasionally surgical scalpel blades.

Despite appearing as a mineral, obsidian is a mineraloid because its rapid cooling prevents a true crystalline lattice from forming. It has been utilized by humans for over tens of thousands of years.

Identified easily by its glassy appearance, sharp conchoidal fracture edges, and opaque black color. Common in western North America and Mediterranean volcanic regions.