A pile of iron filings. Iron is a transition metal element with symbol Fe and atomic number 26. By mass it is the most abundant element on Earth, forming most of the core. It is malleable and ductile, but its properties can be radically altered by alloying. The prehistoric use of iron tools was a turning point in human evolution (the Iron Age). The production of iron and steel formed he basis of the industrial revolution. Iron is also essential in humans, especially in oxygen transport in the blood.