Obsidian

 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. 

A strongly protective stone, it forms a shield against negativity. It blocks psychic attack and absorbs negative energies from the environment. Acts as a reflective shield against negative energy.