What is this spherical black stone?

Ok I know the question is a little vaque, and without a picture this will be hard to judge but.... I found this rock outside, it was a black half sphere about the size of a baseball with a smaller center ball. I decided to clean it and break it open, the outer sphere came off no problem, but the inner sphere (where most of the weight is btw) stays intact. I chipped the small sphere a little and the inside looks like it has tiny crystals or something because it is shiny. To me it just looks like this rock is covered in some type of black dusty substance that has hardened on to it. How could I clean this, or better yet what is it?