Hexahedrite
An iron meteorite low in nickel, made of large kamacite crystals and showing no Widmanstätten pattern.
With a nickel content of typically around 5–6 per cent, hexahedrites sit at the low-nickel end of the iron meteorites. At that composition the metal cools into kamacite, a nickel-poor form of iron-nickel, with almost no taenite. Each specimen can be a single kamacite crystal many centimetres across, so when etched it shows no Widmanstätten pattern at all. The name comes from the hexahedron, or cube, because kamacite tends to break along planes parallel to cube faces.
They matter because their simple structure records events clearly. Nearly all hexahedrites belong to the chemical group IIAB, and most show Neumann lines: fine, straight, intersecting lines produced when shock caused the crystal to twin. Classic examples include Braunau, which fell in what is now the Czech Republic in 1847, and Coahuila from Mexico.
To recognise a hexahedrite, look at an etched, polished face. Instead of criss-crossing bands you will see a uniform, slightly frosted surface crossed by sharp hairline Neumann lines. The meteorite will be heavy and strongly magnetic. Etching uses acids and is strictly for trained adults with proper protection.
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