Freshwater Rock in Saltwater

[stringcheese]

I bought some rock for my freshwater tank that sort of looked like small pieces of flagstone. I can't remember if they said they were for freshwater only, but I have them in a saltwater tank I am setting up.
Should I be worried about this? I've heard to not put lava rock in saltwater, but thats the only kind I've heard to avoid.

 

[killafins]

I heard that rumor too, i wouldn't recommend it