Grounding, Healing, Protecting.
Obsidian is a very protective stone, and is excellent for removing negativity. It is also great protection against psychic attacks. In particular obsidian protects the gentle from abuse, and is used to cut attachment cords to release one. It is a very grounding stone and very healing.
Carry one in your purse/wallet or have near the front door of home, or place in a drawer at work.