Live Rock is the broad taxonomic classification given to rock and reef structure which acts as a host to the many marine organisms that live on and within it. Live Rock is usually comprised of calcium carbonate but it can be made of many different materials including synthetic substances, concrete, and even theĀ aragonite skeletons of ancient stony corals that have since passed on to the big aquarium in the sky. Live Rock is the foundation of our natural coral reefs in the oceans as well as for the aquariums and fish tanks in our homes.