Iron meteorites
Iron meteorites are mostly composed of iron and nickel. They were formed from the cores of small asteroids (planetesimals) that got hot enough to melt and their material separated into layers. This process is called differentiation.
Iron meteorites are further divided into several categories based on the nickel content of the crystal structure:
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Hexahedrites: they contain little nickel (usually less than 6%) and have no visible Widmanstätten structure
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Octahedrites: They have a higher nickel content (6-20%) and are the most common type of iron meteorites. When etched with acid, they show the characteristic Widmanstätten structure
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Ataxites: They have a very high nickel content (more than 16%) and show no visible structure even after acid etching
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