Calcium carbonate (CaCO3) is a naturally abundant, renewable resource that is all around us; it actually makes up 4% of the earth’s crust. Calcium carbonate is found in a variety of sources, including marble, limestone, and chalk and is a foundational building block for snail shells, coral, pearls, and eggshells. Our calcium carbonate is responsibly and sustainably sourced by our stone partner from 180+ locations around the world.