Marge, we need some information and a better picture. You can take a picture with any device but this one gives us no details. We need to be able to enlarge the picture and see details. Also, any information about where it was found can help us. If, for example, the rock was found in Youngstown, Ohio near an iron mine, that would be helpful. We could eliminate things by geographic area, we could support assumptions by trends of minerals commonly found in and around the area. Without testing we need as much information as possible. It really looks like slag. However, if you have a magnet, you can tell us if it is magnetic, you can tell us how hard it is by attempting to scratch it with a fingernail, a pocketknife or a rock of a known hardness like a piece of quartz. We may be able to help with some more info.