Ungrouped irons
Irons that fit no known group: each may represent its own asteroid.
- Classification
- Iron meteorites › Ungrouped irons
- In our catalogue
- 113 meteorites, 4 seen to fall
- Heaviest
- Bacubirito, 22 t
- Earliest recorded fall
- Nedagolla, 1870
- Most recent fall
- Ban Rong Du, 1993
About 15% of iron meteorites do not belong to any recognised group. Many are the only known samples of their parent asteroids, so ungrouped irons alone point to dozens of otherwise unknown melted bodies in the early Solar System.
What makes an iron ungrouped
An iron is called ungrouped when its combination of nickel and trace elements, such as gallium, germanium, iridium and gold, does not fall on the trend of any recognised group. Some ungrouped irons are pairs or small clusters, called grouplets, waiting for more members; others seem to be the only sample of their parent. About 15% of all classified irons are ungrouped.
Their structures range from hexahedrites to ataxites, and some contain silicate inclusions. Isotopes of molybdenum and tungsten show that ungrouped irons come from both the inner and outer Solar System.
Why they matter
Ungrouped irons are the main reason scientists think iron meteorites sample around 50 or more parent bodies. Each truly distinct ungrouped iron may be the only surviving piece of a core whose asteroid has otherwise vanished. They show that core formation was widespread among early planetesimals, and that many of those bodies were destroyed in collisions long ago.
Famous examples
Chinga, from the Tuva region of Siberia, is a nickel-rich ataxite found as many fragments in a stream bed. Mbosi, in Tanzania, is a single mass of about 16 tonnes, still lying where it was found. Bacubirito in Mexico weighs about 22 tonnes and is one of the largest meteorites known. Gebel Kamil, from Egypt, is the iron that made Kamil crater, about 45 m across, first spotted in satellite images in 2008 and among the best-preserved small impact craters on Earth; about 1.6 tonnes of fragments have been recovered. Dronino, from Russia, is a nickel-rich iron found as many weathered masses. Nedagolla, which fell in India in 1870, is one of the few ungrouped irons seen to fall.
How to recognise one
Ungrouped irons look like any other iron meteorite: heavy, magnetic and metallic beneath their crust or rust. Only chemical analysis shows that they belong to no group. When enough similar ungrouped irons accumulate, they can become a new group, as happened with the IIG irons.
Iron meteorites are often found by metal detectors, especially in deserts and farmland. Anyone searching must have the landowner's permission and follow local laws, which in some countries make meteorites the property of the state.
Famous examples
- Chinga Iron, ungrouped, Russia, 1913 · 209.4 kg
- Mbosi Iron, ungrouped, Tanzania, 1930 · 16 t
- Bacubirito Iron, ungrouped, Mexico, 1863 · 22 t
- Gebel Kamil Iron, ungrouped, Egypt, 2009 · 1.6 t
- Dronino Iron, ungrouped, Russia, 2000 · 40 kg
- Deep Springs Iron, ungrouped, United States, 1846 · 11.5 kg
- Nedagolla Iron, ungrouped, India, 1870 · 4.5 kg
- Mont Dieu Iron, ungrouped, France, 1994 · 360 kg
Related groups
- IAB irons Irons with stony inclusions, from a partly melted asteroid. Canyon Diablo and Campo del Cielo.
- IVB irons Nickel-rich ataxites. Hoba, the largest meteorite, is one.
- IIG irons Low-nickel irons with large crystals of schreibersite.
- 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).