Neumann Lines

Fine twinning boundaries seen as parallel lines running along the plane of kamacite crystals of hexahedrite iron meteorites. They may appear also in octahedrite iron meteorites provided the kamacite phase is about 30 mm wide. They can be seen after a polished meteorite cross-section is treated with acid. The lines are indicative of a shock-induced deformation of the kamacite crystal, and are thought to be due to impact events on the parent body of the meteorite.

Per Norton in Rocks from Space:

They would normally be invisible to the naked eye, but the kamacite crystal has apparently suffered intense shock , cause the the crystal lattice to slip along planes parallel to the face of the hexahedron. This slippage makes the twinning planes become visible as parallel lines and demonstrates that hexahedrites have suffered impact shock in space and were probably broken along natural cleavage planes of the original large kamacite crystals.