DIY LIVE ROCK

The rock in my tank is grey and very porous. I never thought that this could be concrete untill I read a post this week about making your own lr. Since this rock has been used in the tank for several months now is it possible that its live. I have sand in my tank that is a year old, but not the live stuff. At the lfs is see bags of live sand is it any good? Thanks again.
 
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