IID irons
Fine to medium octahedrites rich in gallium and germanium.
- Classification
- Iron meteorites › IID irons
- Share of witnessed falls
- about 0.3%
- In our catalogue
- 21 meteorites, 3 seen to fall
- Heaviest
- Carbo, 454 kg
- Earliest recorded fall
- Elbogen, 1399
- Most recent fall
- N'Kandhla, 1912
IID irons are fine to medium octahedrites with about 10–11% nickel and high gallium and germanium. They are a magmatic group, from a single asteroid core.
Mineralogy and chemistry
IID irons contain about 9.6% to 11.3% nickel and are fine to medium octahedrites. They have the highest gallium of any iron group, roughly 70 to 85 parts per million, and high germanium, with schreibersite common as large crystals and rods. Their trace elements follow a magmatic trend, showing crystallisation of a core.
Isotopes of molybdenum and tungsten place IID in the 'carbonaceous' family, linking it to the outer Solar System, like the IIC, IIF, IIIF and IVB irons.
Parent body and formation
IID irons come from one asteroid core that formed early, within a few million years of the first solids. Their cooling rates indicate a core buried under a mantle, cooling over tens of millions of years. The high gallium and germanium content suggests that the parent body kept more of these moderately volatile elements than most iron parent bodies did.
Abundance and famous examples
IID has about twenty members. It includes two historic falls in central Europe. Hraschina fell near Zagreb, in present-day Croatia, on 26 May 1751; two masses of about 40 kg and 9 kg were recovered and taken to Vienna, and the event became one of the key cases Ernst Chladni used in 1794 to argue that meteorites fall from space. Elbogen, a mass of about 107 kg kept for centuries in the castle at Loket in Bohemia, is said by legend to have fallen around 1400. Carbo from Mexico, about 450 kg, and Wallapai, about 430 kg, from Arizona, are large finds, and Needles and Rodeo are others.
How to recognise one
IID irons look like typical fine to medium octahedrites, heavy and magnetic, with a neat, narrow Widmanstätten pattern when etched. Large schreibersite crystals may show as pale, brittle inclusions. Analysis for gallium and germanium identifies the group.
Why they matter
The historic IID falls helped prove the reality of meteorites, and the group now plays a part in tracing how cores formed in the outer Solar System. Comparing IID metal with that of other carbonaceous-family irons shows how varied the raw materials of those distant bodies were.
Famous examples
- Carbo Iron, IID, Mexico, 1923 · 454 kg
- Wallapai Iron, IID, United States, 1927 · 430 kg
- Needles Iron, IID, United States, 1962 · 45.3 kg
- Rodeo Iron, IID, Mexico, 1852 · 44 kg
- Elbogen Iron, IID, Czechia, 1399 · 107 kg
- Hraschina Iron, IID, Croatia, 1751 · 49 kg
Related groups
- IIC irons A rare group of plessitic octahedrites.
- IIF irons A small group of magmatic irons.
- IIIAB irons The most common iron meteorites: medium octahedrites from one asteroid core.
- 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).