Hav you ever held a jet stone? It is extremely light and will even sometimes float in water. It is said to help cleanse the energetic gateway, associated with the kidney.
It is a black stone, that is said to be protective for the physical body as well as the psychic body. It is grounding and is said to help break poor behavioral patterns.
It is said to be good to help those with migraine or headaches and is an all around lovely stone to work with.