Neumann lines
Fine, straight parallel lines in kamacite caused by shock twinning, seen on etched iron meteorites.
Neumann lines are sets of very thin, straight lines that cross kamacite crystals in many iron meteorites. They are mechanical twins: narrow slabs of the crystal that were sheared into a mirror-image orientation when the metal was struck by a sudden shock, most likely during a collision in space. Because kamacite can twin along several planes, the lines often appear in two or more directions, crossing each other.
They are useful as a simple record of shock history. Their presence shows the metal was jolted at relatively low temperature, while their absence in some irons may mean there was no such shock or that later heating erased them. They are named after Johann Neumann, who described them in the Braunau iron soon after its fall in 1847. They are especially clear in hexahedrites, which are essentially single kamacite crystals, and in the broad kamacite of coarse octahedrites such as Sikhote-Alin.
To spot Neumann lines, look at an etched slice under a raking light or hand lens. They look like hairline scratches, but they are perfectly straight, run in fixed directions within each crystal and stop at crystal boundaries.
Related terms
Level: Enthusiast Teens and adults