Obsidian

Hardness 5 to 5.5 on the Mohs scale, dark black or smoky color, vitreous luster, amorphous crystal structure with conchoidal fracture, specific gravity around 2.4.

Formed by the rapid cooling of felsic lava extruded from a volcano without crystal growth, occurring worldwide wherever volcanic activity has taken place.

Used historically for sharp cutting tools like arrowheads and blades, and currently utilized in decorative objects, jewelry, and experimental surgical scalpel blades.

Due to its lack of crystal structure, obsidian breaks with exceptionally sharp edges known as conchoidal fractures, sometimes sharper than modern steel surgical blades.

Identified by its glossy, glass-like appearance, dark coloration, and distinct curved conchoidal fracture patterns. Commonly found near recent volcanic flows in western North America and Mediterranean regions.