IIF irons
A small group of magmatic irons.
- Classification
- Iron meteorites › IIF irons
- Share of witnessed falls
- about 0.1%
- In our catalogue
- 6 meteorites, 1 seen to fall
- Heaviest
- Monahans (1938), 27.9 kg
- Earliest recorded fall
- Repeev Khutor, 1933
IIF is a small magmatic group of irons with distinctive trace-element patterns. Only a handful are known.
Mineralogy and chemistry
IIF irons have relatively high nickel, roughly 10% to 14%, and are plessitic or fine octahedrites, or have anomalous structures. Their trace elements form a magmatic trend, and they are poor in some moderately volatile elements compared with groups of similar nickel content. Isotopes place them in the 'carbonaceous' family of meteorites from the outer Solar System.
Their metal chemistry is very similar to the metal in the Eagle Station pallasites, which has led to the suggestion that both come from the same parent body: the irons from its core, the pallasites from where metal met olivine.
Parent body and formation
If the IIF irons and Eagle Station pallasites share a home, it was a melted body made from carbonaceous chondrite-like material, oxidised enough for some iron to stay in the silicates as iron-rich olivine. The relatively high nickel of IIF metal fits such oxidising conditions, which leave less iron available to form metal. The exact relationship is still being tested with isotopes of chromium, molybdenum and oxygen.
Abundance and famous examples
IIF is a small group of about half a dozen members. Repeev Khutor, which fell in the Astrakhan region of Russia on 8 August 1933, is the only fall; about 7 kg was recovered. Del Rio, Monahans (1938) and Corowa from New South Wales are among the finds. Some are small, and new members are occasionally recognised as more irons are analysed.
How to recognise one
IIF irons are heavy, magnetic masses that etch to a fine or plessitic pattern. They look like many other nickel-rich irons, so only trace-element analysis can assign one to the group.
Why they matter
Matching irons to pallasites from the same body lets scientists build a fuller picture of one differentiated asteroid. For IIF and the Eagle Station grouplet, that picture would be of a body from the outer Solar System, a rare chance to see how a carbonaceous world formed its core.
Small groups like IIF also show how many separate iron parent bodies existed. Each one, however few its members, is a separate core that once lay inside its own melted asteroid, adding to the long list of early worlds since broken apart.
Famous examples
- Repeev Khutor Iron, IIF, Russia, 1933 · 7 kg
- Del Rio Iron, IIF, Mexico, 1965 · 3.6 kg
- Monahans (1938) Iron, IIF, United States, 1938 · 27.9 kg
- Corowa Iron, IIF, Australia, 1964 · 11.34 kg
- Dorofeevka Iron, IIF, Kazakhstan, 1910 · 12.6 kg
Related groups
- Eagle Station pallasites A tiny grouplet of pallasites with iron-rich olivine and nickel-rich metal, from a separate parent body.
- IIC irons A rare group of plessitic octahedrites.
- IID irons Fine to medium octahedrites rich in gallium and germanium.
- Iron meteorites Almost pure iron-nickel metal, mostly from the cores of asteroids that melted and were later shattered.
Photos shared under Creative Commons licences (Wikimedia Commons).