Tetrataenite
An ordered iron–nickel alloy that forms only with extremely slow cooling, and a natural rare-earth-free magnet.
Key facts
- Formula
- FeNi
- Family
- Metals and alloys
- Crystal system
- Tetragonal
- First described
- meteoritic metal, 1980
Tetrataenite was described as a mineral in 1980 from meteorites, after studies of the rims of taenite ribbons. It forms only with millions of years of slow cooling, so it is found almost nowhere except meteorites.
What it is
Tetrataenite has equal numbers of iron and nickel atoms arranged in alternating layers. The ordering can take place only below about 320 °C and so slowly that it needs millions of years. It is a very strong permanent magnet.
Where it is found
It forms the outermost rims of taenite ribbons in octahedrites and occurs in the metal of ordinary chondrites and mesosiderites. Its magnetism has been used to read the history of magnetic fields in asteroid cores.
How it is recognised
It is identified by its nickel content of about 50% and its ordered structure under the electron microscope. Its magnetic signature can be mapped.
Did you know?
Researchers have tried to make tetrataenite artificially as a magnet that needs no rare earth elements.
Magnetism in tetrataenite from meteorites shows that some asteroid cores generated magnetic fields, like Earth's.