Iron is a chemical element with the symbol FE and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust.' Iron is a chemical element with the symbol FE and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. By mass, it is the most common element on Earth, forming much of Earth's outer and inner core. It is also the fourth most common element in the Earth's crust. The three-letter abbreviation for iron is 'FE, ' which is derived from its Latin name ferrum.