Animal Essentials' Calcium is a natural calcified red seaweed (Lithothamnium sp.) that contains a wide variety of essential nutrients, including calcium, magnesium, boron and zinc. It is harvested from the seabed off the coast of Iceland, where each batch is cleaned, heat processed and tested for purity by an analytical laboratory. Calcium carbonate, the form of calcium found in Seaweed Calcium, is one of the most challenging essential minerals for the animal body to utilize For instance, the calcium carbonate contained in bone meal is only about 45% available to the body. However, because of the unique honeycomb-like porosity of the tiny particles that comprise Seaweed Calcium, the calcium carbonate it contains is up to 70% bioavailable.