Zinc is a brittle, bluish-white metal. When exposed to air, it quickly tarnishes with an encroaching film of zinc oxide. It is one of the most vital trace elements, and is involved in many reactions that occur in the body, such as the conversion and excretion of carbon dioxide. This chemical is found in blood cells, muscle tissues, bones, kidneys, the liver, and even the retinas! It is also used to protect ships and machines from corrosion.