In the metal cores of partially molten asteroids, iron-nickel alloys crystallized in a distinctive pattern known as the Widmanstätten structure. This pattern is named after one of the first people to observe it some 200 years ago, Count Alois de Widmanstätten. The pattern forms only deep inside planetary bodies that take millions of years to cool. Iron never crystallizes this way on Earth's surface, so any metal showing this pattern on Earth is definitely from a meteorite.
The crystal patterns in iron meteorites range from very coarse to extremely fine. The thickness of the crystals in the pattern depends mainly on the amount of nickel they contain, and how slowly the metal cooled. With this information, one can estimate the size of the meteorite's parent body, because larger asteroids cool more slowly than small ones.
Topic: Earth Science
Keywords: Asteroids, Astrogeology, Astrophysics, Crystals, Iron-nickel alloys, Meteorites, Iron, Mineralogy