Obsidian is one of the important type of rocks. If we have to define Obsidian in general, Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly with minimum crystal growth. Obsidian comes under Igneous Rocks. All Igneous Rocks have similar properties and formation process. Along with Obsidian Definition, know more about the History of Obsidian, Etymology of Obsidian in next sections.