Safe to use as base rock?

[darknes]

I was at my LFS looking for base rock, and they have this rock called "Lace rock". It looks similar to live rock, but with less holes and more dense. I was assuming that base rock was a white color, while this lace rock is more grey like concrete.
Is this rock safe to use for saltwater? The person working at the LFS said it is, but it wasn't the owner who I trust, so I don't know.
Any opinions?

 

[fgcu14]

I would assume so. After all I have read posts on how people make their own rock out of concrete mix!

 

[tx reef]

It sounds like the same stuff I got a my LFS when I set up my tank.
No problems from it. Just be sure and boil it and scrub it off real good.