What is Calcite / Grounded Calcium carbonate (GCC) ? Calcium carbonate, or CaCO3, is one of the most useful and versatile materials known to man. It is extremely common and found throughout the world in sedimentary, metamorphic and igneous rocks. Some geologists consider it to be a “ubiquitous mineral” – one that is found everywhere. It comprises more than 4% of the earths crust and is found throughout the world.