Widmanstätten pattern
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Widmanstätten patterns, also known as Thomson structures, are figures of long phases of nickel–iron, found in the octahedrite shapes of iron meteorite crystals and some pallasites.
Segment of the Toluca meteorite, about 10 cm wide
Widmanstätten pattern in the Staunton meteorite
The fine Widmanstätten pattern (lamellae width 0.3mm) of a Gibeon meteorite.
Etched slice of a Canyon Diablo meteorite showing a Widmanstätten pattern
Kamacite
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Kamacite is an alloy of iron and nickel, which is found on Earth only in meteorites. According to the International Mineralogical Association (IMA) it is considered a proper nickel-rich variety of the mineral native iron. The proportion iron:nickel is between 90%:10% and 95%:5%; small quantities of other elements, such as cobalt or carbon may also be present. The mineral has a metallic luster, is gray and has no clear cleavage although its crystal structure is isometric-hexoctahedral. Its density is about 8 g/cm3 and its hardness is 4 on the Mohs scale. It is also sometimes called balkeneisen.
Widmanstätten pattern showing the two forms of nickel-iron minerals, kamacite and taenite
Kamacite and taenite after taenite, exhibiting the octahedral structure of taenite, Nantan (Nandan) iron meteorite, Nandan County, Guangxi Zhuang Autonomous Region, China. Size: 4.8×3.0×2.8 cm. The Nantan irons, a witnessed fall in 1516, have a composition of 92.35% iron and 6.96% nickel.