If you are new to the hobby I suggest getting cured live rock from a LFS to make your cycle a lot faster. If not you can buy more porous dry dead rock from amazon and cycle with it. Looking at that rock, I would only use for freshwater for a planted tank and not in my reef tank. It is heavy since its more dense, and therefore would not be suitable for hosting beneficial nitrifying bacteria. I can't tell its composition by looking at it, but I'd be cautious about using it. Good luck.