Looks more like a base type rock to me, as you add more rock you'll get some more porous stuff that you can easily stack on that rock, the stuff you have in there may make it a bit easier on you to build some nice caves, etc. because it has some flat surfaces...Not necessarliy the prettiest rock in the world, but on the bottom of your rock piles, it definitely serves it's purpose. I've got plenty of rock in my tank that looks similar, you'd never even know it was in there. But it is, and it's supporting the other rock giving it alot of stability.