Newbie wondering if I can use these as base rock?

hi first time poster but I've been lurking awhile, I have about 10kg of coral that I think is man made or looks it anyway I have no idea what material
It's made off but it's been in a fresh water tank.

Could I use it as a base rock and seed it with some live rock? From what I've read anything in the tank will turn "live" with enough time or am I mistaken?

Ild send a photo but I have no idea how anyway sorry for the noob questions