Sample of the element iron Fe rotating. Iron has the atomic number 26, and is a soft transition metal. It is the most common element by mass in the Earth as a whole, and the fourth most common in the crust. It is the most widely_used metal in industry, where it is generally alloyed to form steels of various hardnesses and other properties. It is also the key component of haemoglobin in the blood, which allows oxygen to be transported around the body.