Definition - What does Obsidian mean?
Obsidian is a naturally existing volcanic glass that develops as an extrusive igneous rock. It is formed when the felsic lava ejected from a volcano cools up instantly with a minimum growth of crystal. It is frequently found within rhyolitic lava flow margins called Obsidian flows in which the composition injects a high polymerization and viscosity degree of lava. It is brittle and hard and fractures can produce sharp edges which can be used as surgical scalpel blades.
Petropedia explains Obsidian
Obsidian is a rock produced as a result of rapidly cooled lava. It is considered as a mineral-like rock but not actually mineral because it is not crystalline. It consists of about 70 percent of silicon dioxide. The crystalline rocks that are composed of Obsidian are rhyolite and granite. A pure Obsidian rock is generally dark in color but varies based on the presence of impurities. Magnesium and iron give a color of dark brown to black to the obsidian. The conchoidal fractures of Obsidian rock can produce sharp edges that can be used as arrows and knives making it essential an archaeological material.