For an explanation of differentiation, see the “achondrites” page. Retrieved 31 December 2012.Iron meteorites can be divided into two main groups: those that formed in the cores of large differentiated bodies, and those that didn’t. Bottke Alberto Cellino Paolo Paolicchi (eds.). "Meteoritic Parent Bodies: Their Number and Identification" (PDF). "Rapid accretion and differentiation of iron meteorite parent bodies inferred from 182Hf–182W chronometry and thermal modeling". ^ Qin, Liping Dauphas, Nicolas Wadhwa, Meenakshi Masarik, Jozef Janney, Philip E.
"the IAB iron-meteorite complex: A group, five subgroups, numerous grouplets, closely related, mainly formed by crystal segregation in rapidly cooling melts".
"Formation and exposure history of non-magmatic iron meteorites and winonaites: Clues from Sm and W isotopes". Meteorites and the early solar system II. "Systematics and Evaluation of Meteorite Classification" (PDF). "The effect of Ni on element partitioning during iron meteorite crystallization". The following table shows the groups are described as nonmagmatic and their classification: The IIE meteorites are now classified as regular achondrites. Two of those groups, the IAB and the IIICD meteorites are now classified as primitive achondrites. Other iron meteorites can also contain silicate inclusions but with different mineralogy (IVA for example has tridymite and pyroxene). They share a number of similarities, the most easily recognizable is that they contain many silicate inclusions composed of olivine, pyroxene and feldspar. Three iron meteorite groups are described as being part of the nonmagmatic meteorites. The term "nonmagmatic" is still sometimes used to refer to this grouping of meteorites, although its use is now deprecated.
The most likely cause for this to happen are impact events. Today, the processes that lead to these unusual properties are described as partial melting and subsequent fast cooling, which prevented melt migration. In the 1970s, it was realized that some of the iron meteorite groups had properties that were incompatible with this formation mechanism, leading some scientists to posit that they were not formed through this mechanism. While the parent body of the meteorites cools off, the metallic core crystallizes into meteoric iron, an iron- nickel alloy. The formation of metallic cores depends on the heat of radionuclides that lead to melting and differentiation into a core and a silicate mantle. Iron meteorites are derived from planetary cores of asteroids and planetesimals. The meteorites that were described to be nonmagmatic are now understood to be the product of partial melting and impact events and are grouped with the primitive achondrites and the achondrites. Today, the terms are still sometimes used, but usage is discouraged because of the ambiguous meanings of the terms magmatic and nonmagmatic. The concept behind this was developed in the 1970s, but it was quickly realized that igneous processes actually play a vital role in the formation of the so-called "nonmagmatic" meteorites. Nonmagmatic meteorite (also nonmagmatic iron meteorite) is a deprecated term formerly used in meteoritics to describe iron meteorites that were originally thought to have not formed by igneous processes, to differentiate them from the magmatic meteorites, produced by the crystallization of a metal melt.