IC irons
A small magmatic group of coarse octahedrites, low in nickel.
- Classification
- Iron meteorites › IC irons
- In our catalogue
- 12 meteorites
- Heaviest
- Bendegó, 5.36 t
IC irons are a small group, mostly coarse octahedrites or coarser, with about 6.1–6.8% nickel. They are magmatic: they formed as the core of a melted asteroid crystallised.
Mineralogy and chemistry
IC irons contain about 6.1% to 6.8% nickel and are mostly coarse octahedrites, though some show anomalous structures. They are relatively low in gallium and germanium for low-nickel irons and contain cohenite, the iron carbide, as well as troilite and schreibersite. Their iridium falls sharply as other elements change, a magmatic trend: the group formed as the core of a melted asteroid crystallised.
Chemically, IC irons sit between the IAB irons and the IIAB irons on plots of gallium and germanium against nickel, and they are distinguished by a combination of elements rather than any single one.
Parent body and formation
IC irons come from one asteroid core. Their trace-element trends show crystallisation of a sulphur-rich metallic liquid from the outside inwards. The core probably belonged to a body in the inner Solar System, as isotopes of molybdenum and other elements place IC irons in the 'non-carbonaceous' family. Their cooling rates and size of parent are less well known than for the big groups, because so few samples exist.
Abundance and famous examples
IC is a small group, with about a dozen members, none seen to fall. Bendegó, found in Bahia, Brazil, in 1784, weighs about 5.4 tonnes and is the largest meteorite found in Brazil. It was moved with great difficulty to Rio de Janeiro in 1888 and survived the fire that destroyed much of the National Museum there in 2018. Murnpeowie, a 1.1-tonne mass from South Australia found in 1909, is famous for its deeply sculpted regmaglypts. Mount Dooling from Western Australia, Arispe from Mexico and Etosha from Namibia are other members.
How to recognise one
IC irons look like any coarse octahedrite: heavy, magnetic, with a coarse pattern when etched. Only trace-element analysis separates them from IAB or IIAB irons.
Why they matter
Each magmatic iron group adds one core to the count of melted asteroids. The IC irons are a reminder that even a small, rarely studied group samples a whole body that once had a crust, mantle and core, now lost except for these masses of metal.
Famous examples
- Bendegó Iron, IC, Brazil, 1784 · 5.36 t
- Murnpeowie Iron, IC, Australia, 1909 · 1.14 t
- Mount Dooling Iron, IC, Australia, 1909 · 734 kg
- Arispe Iron, IC, Mexico, 1896 · 683 kg
- Etosha Iron, IC, Namibia, 1970 · 110.7 kg
- Chihuahua City Iron, IC, Mexico, 1929 · 54 kg
Related groups
- IAB irons Irons with stony inclusions, from a partly melted asteroid. Canyon Diablo and Campo del Cielo.
- IIAB irons Hexahedrites and coarsest octahedrites, including Sikhote-Alin.
- Iron meteorites Almost pure iron-nickel metal, mostly from the cores of asteroids that melted and were later shattered.
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