Black Obsidian Tumblestone from Mexico
This one is the power house when it comes to protecting from negative energy! 
I great crystal to place in protection grids in and around the home.
On a personal level, if working with Black Obsidian for the first time, it may feel quite intense as you may be faced with all your own ‘stuff’ initially. But once you work through the healing, releasing of limiting patterns etc, it truly is a beautiful crystal to work with and even somewhat comforting.