Fe – iron – is a silver-white metal with a wide range of applications. It is the second most common metal in the Earth's crust after aluminum. In its pure form, iron is a soft, malleable substance that rusts easily when exposed to air and moisture. Iron gains its hardness and strength when alloyed with different elements such as carbon. Iron and carbon are combined to make an alloy called steel, which is used to make cars, ships, buildings, tools, pots and pans, and even more. It is also an important trace element for people and animals. Iron is a component of hemoglobin, a protein in our blood that helps transport oxygen from the lungs to other areas of the body. Iron deficiency can lead to feelings of fatigue and weakness.