Kamacite bandwidth
Kamacite bandwidth is the width of the kamacite plates in an octahedrite, used to sort them from coarsest to finest.
In an etched octahedrite iron meteorite, the Widmanstätten pattern is made of crossing plates of kamacite. Their width, measured at right angles to the plates, is the kamacite bandwidth. It depends mainly on the nickel content of the metal and on how slowly it cooled: lower nickel and slower cooling give broader bands.
Octahedrites are classed by bandwidth. Coarsest octahedrites have bands wider than 3.3 millimetres, coarse 1.3 to 3.3 millimetres, medium 0.5 to 1.3, fine 0.2 to 0.5 and finest below 0.2 millimetres. Plessitic octahedrites have even thinner, spindle-like plates. Gibeon is a fine octahedrite, while Sikhote-Alin, a coarsest octahedrite, often shows a very broad, almost hexahedrite-like structure.
Bandwidth gives a structural class, which is different from the chemical group. Many groups have typical bandwidths, so the structure is a helpful clue, but scientists rely on chemistry for formal classification.
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