Obsidian is one of my favorite stones- so far! It comes in several different colors besides black and snowflake- like blue, rainbow, gold sheen, mahogany- and another form- Apache tear. Each has it's qualities, which you can look at in any crystal book, but for general things that I've noticed- unbelievably grounding and calming. It helps me deal with pain and anger, grudges, any emotions that I am holding on to. It can help with trauma, psychic attack, psychic overload, overstimulation, chaos... it will show you what is hidden, making it a great seerstone. It can be rather ruthless in showing the truth however. It is so useful for psychic and sensitive people.