Editing Widmanstätten pattern (section)

{{Short description|Crystal patterns found in some meteorites
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{{Use American English|date=June 2019}}
{{Use mdy dates|date=June 2019}}
[[File:TolucaMeteorite.jpg|thumb|300px|Segment of the [[Toluca (meteorite)|Toluca meteorite]], about 10 cm wide]]
{{Steels}}

'''Widmanstätten patterns''' {{IPAc-en|ˈ|v|ɪ|d|m|ɑː|n|ˌ|ʃ|t|eɪ|t|ɪ|n}} ({{respell|VID|man|shtay|tin}}), also known as '''Thomson structures''', are figures of long [[Phase (matter)|phases]] of [[nickel]]–[[iron]], found in the [[octahedrite]] shapes of iron meteorite crystals and some [[pallasite]]s. 

[[Iron meteorite]]s are very often formed from a single [[crystal]] of iron-nickel alloy, or sometimes a number of large crystals that may be many meters in size, and often lack any discernable crystal boundary on the surface. Large crystals are extremely rare in metals, and in meteors they occur from extremely slow cooling from a molten state in the vacuum of space when the [[Solar System]] first formed. Once in the solid state, the slow cooling then allows the [[solid solution]] to [[Precipitation (chemistry)|precipitate]]  a separate phase that grows within the [[crystal lattice]], which form at very specific angles that are determined by the lattice. In meteors, these [[interstitial defect]]s can grow large enough to fill the entire crystal with needle or ribbon-like structures easily visible to the naked eye, almost entirely consuming the original lattice. They consist of a fine interleaving of [[kamacite]] and [[taenite]] bands or ribbons called ''[[Lamella (materials)|lamellae]]''. Commonly, in gaps between the lamellae, a fine-grained mixture of kamacite and taenite called [[plessite]] can be found.<ref>''Encyclopedia of the Solar System'' by Tilman Spohn, Doris Breuer, Torrence V. Johnson -- Elsevier 2014 Page 632</ref> 

Widmanstätten structures describe analogous features in modern steels,<ref>Dominic Phelan and Rian Dippenaar: Widmanstätten Ferrite Plate Formation in Low-Carbon Steels, METALLURGICAL AND MATERIALS TRANSACTIONS A, VOLUME 35A, DECEMBER 2004, p. 3701</ref> titanium, and zirconium alloys, but are usually microscopic in size.