Can any rock be base rock?

is the rock in the pic what you want to add if it is sand stone it will work as I would put it into a bucket of salt water for a week and then test for Fe (iron) and Cu (Copper). I have use different rock but that was many years ago. Petrified wood in most cases is ok and Jade is great way to keep valubale sone out of harms way but you may want a lion fish in there also as a deturent. I wonce had a chunk of jade in a salt tank looks great but seems it was worth about $5000 I put a farly large lion in with it. The fish would sit right on top of the piece of jade.
If you don't have calcium carbonate rock type of rock you want to make sure it does not contain and metals that can leach in to the tank and kill off inverts.

Bill