Here are a couple of images from a slice of the Gibeon iron meteorite that fell in Namibia, South Africa in pre-historic times. It is composed of ~90% iron, ~8% nickel, 0.4% cobalt and 0.04% phosphorus. It is classed as a type IVA (said as 4A) fine octahedrite. Radiometric dating indicates that crystallization of the Gibeon iron-nickel took place approx. 4 billion year ago.
So, the structure we are seeing in these photos was created 4 billion years ago - older than any known (surviving) rock on Earth.
Iron meteorites are believed to be part of the smashed-up core of large asteroids or small planetoids.
This slice has been polished and etched (with weak acid) to bring out the Widmanstätten pattern. This pattern is individually unique to every iron meteorite (as it relates to the rate of cooling of the parent asteroid). It only occurs in meteorites and cannot be duplicated in a lab because its creation requires that cooling take place over millions of years. The pattern is caused by the intergrowth/segregation of the two nickel-iron minerals, kamacite (the light bands) and taenite (the dark bands) as the core of the parent asteroid slowly cooled.
Note: The more true color is shown in pic2 as I converted pic1 to greyscale in order to get it under the 200 Kb forum limit (without losing too much detail).
Bruce
You know I just read an article the other day about astroids. Seems that there are quite a number that have the possiblity of striking the earth, about 1,500 of them. Though they said that the chances are one in a million that it would happen. However consider this, one in a million is pretty good odds when you consider all the stuff floating around out in space. 
