Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. Obsidian is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth.  In the past, obsidian was used to manufacture cutting and piercing tools and it has been used experimentally as surgical scalpel blades.  Obsidian is rated between 5 and 6 on the Mohs hardness scale.  Obsidian is associated with resolution and remedies shock, trauma and blockage stone and associated with root chakra. Obsidian is also thought to aid in healing ailments and balancing energy in the physical body.