Iron meteorites are parts of the cores of former protoplanets or bigger asteroids. They were formed about 4.5 billion years ago, making these meteorites much older than the oldest rocks here on Earth. When the protoplanet from which the iron meteorite came was still completely molten, all heavier elements (mainly iron) sunk down to the centre of the body building a metallic core that was surrounded by lighter, rocky material (the mantle and crust). The Earth went through the same process in its beginning, only we will never be able to hold a piece of the Earth's iron core in our hands.
The protoplanet later got destroyed in a heavy collision with another celestial body exposing the iron core. Finally - after a long voyage through outer space - a small piece of this iron core fell on Earth as a new iron meteorite.
Meteorites.org shows a collection of beautiful meteorites which can be acquired on