| Iron meteorites originate from the cores of differentiated asteroids, those large enough to cause complete melting during formation so that the high density iron sinks to the centre. The metal is a mixture of alloys of iron and nickel with other trace elements. Iron meteorites have a variety of crystalline structures which depend on the ratio of iron to nickel and the rate at which it cooled on the parent body. Classification of irons into groups depends on this crystalline structure and their chemical composition. Often iron meteorites are sliced and etched with acid, this reveals the crystalline structure visible as the Widmanstatten pattern, although BIMS members like to recognise the earlier work of G. Thomson! (Image shows a close-up of the Thomson structures (more often called the Widmanstatten pattern) in an etched slice of Gibeon, IVA)
|  |
