Widmanstatten Microstructures in Meteorites
H. K. D. H. Bhadeshia
Meteorites are essentially iron-nickel alloys with 4-25 wt% of nickel. They have their origins in asteroids which break up by collision and some of the fragments make it to Earth. During their evolution, they begin in the molten state, solidify and then cool incredibly slowly (about 1 K in a million years). The austenite that exists at high temperatures eventually cools to generate a Widmanstatten pattern of ferrite plates in a matrix of residual austenite. In the earth sciences, the ferrite is known as kamacite, and the austenite as taenite.
The photographs below were taken at the Smithsonian Musuems in Washington, USA. They can be enlarged by clicking on the thumbnails.
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Widmanstatten ferrite
