Copper can be found as a metal in the ground. Normally, it is green on the outside. Most copper is not as a metal but in chemical compounds. Chalcopyrite is the most common copper ore. It is a mixture of pyrite and copper sulfide. Copper is found in small amounts in living things. Some mollusks and arthropods have blue blood because they have copper in their blood. Animals such as humans and other mammals have red blood because it contains iron.