I'd trash those and get yourself some nice live rock. I think that's artificially-created sandstone. Dunno how it'd react with saltwater, but it's basically useless even if it is safe. It provides no hiding places for small animals such as pods and has pitifully little surface area for bacteria.
I have live rock already I was just curious as to if it was safe for saltwater for the just for looks and appearance. Ok thank you do you know if it's ok for fresh water because we have a 55 gallon that's gonna be up and running soon?