All my pics are too big. I think its key largo rock. Its heavy and has a feel of rough concrete. Looks like something out of the sea. My friend had it in a tank full of Oscars but I don't want to stick something in that changes my water
You could try uploading to photobucket and pasting in a link instead.
I don't fancy the sound of concrete at all...constant exposure to water could make it crumble over time releasing powdery and all sorts of other unknown stuff.