Obsidian is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Obsidian is produced from felsic lava, rich in the lighter elements such as silicon, oxygen, aluminum, sodium, and potassium. 
Obsidian is used for grounding, healing, and protection. Physically the inky black stone is used for keeping your circulation in flow and encourages your deep tissues to heal. Emotionally it keeps negative energies, thoughts and feelings at bay and helps you to embrace the courage to explore the unknown.