| Nonmagmatic meteorite | |
|---|---|
| — Class — | |
 Goose Lake Meteorite is an IAB meteorite in the sLL subgroup (low-Au, low-Ni) | |
| Compositional type | Iron |
| Type | Iron |
| Subgroups | |
| Alternative names | Nonmagmatic iron meteorites |
Nonmagmatic meteorite (alsononmagmatic iron meteorite) is a deprecated term formerly used inmeteoritics to describeiron meteorites that were originally thought to have not formed byigneous processes, to differentiate them from themagmatic meteorites, produced by the crystallization of a metal melt.[1] 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. Today, the terms are still sometimes used, but usage is discouraged because of the ambiguous meanings of the terms magmatic and nonmagmatic. 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 theprimitive achondrites and theachondrites.[2]
Iron meteorites are derived fromplanetary cores of asteroids andplanetesimals. The formation of metallic cores depends on the heat ofradionuclides that lead to melting anddifferentiation into a core and asilicate mantle. While theparent body of the meteorites cools off, the metallic core crystallizes intometeoric iron, aniron-nickelalloy.[1]
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.[2]
Today, the processes that lead to these unusual properties are described as partial melting and subsequent fast cooling, which prevented melt migration.[3] The most likely cause for this to happen are impact events.[3][4]
The term "nonmagmatic" is still sometimes used to refer to this grouping of meteorites, although its use is now deprecated.[5]
Threeiron meteorite groups are described as being part of the nonmagmatic meteorites. They share a number of similarities, the most easily recognizable is that they contain manysilicate inclusions composed ofolivine,pyroxene andfeldspar. Other iron meteorites can also contain silicate inclusions but with different mineralogy (IVA for example hastridymite andpyroxene).[6] Two of those groups, theIAB and theIIICD meteorites are now classified as primitive achondrites. The IIE meteorites are now classified as regularachondrites.[2]
The following table shows the groups are described as nonmagmatic and their classification:
| Group | Currently classified as | Compositional type |
|---|---|---|
| IAB | Primitive achondrite[2] | Iron meteorite |
| IIICD | Primitive achondrite[2] | Iron meteorite |
| IIE | Achondrite[2] | Iron meteorite |