Yeah... strange things happen when you move too far from your spawn point shortly after the world begins generating.
It's not in the pic, but there's some exposed coal too. This piece of stone is completely exposed, and as far as I can tell there aren't any tunnels or holes in it. I found it while the world was still not-quite-generated, so I'm thinking it's some kind of bizarre error. I haven't started digging in it yet, so I don't know how prevalent other materials are in it.