Neumann Lines
Fine twinning boundaries seen as parallel lines running along the plane of kamaciteMore common than taenite, both taenite and kamacite are Ni-Fe alloys found in iron meteorites. Kamacite, α-(Fe,Ni), contains 4-7.5 wt% Ni, and forms large body-centered cubic crystals that appear like broad bands or beam-like structures on the etched surface of a meteorite; its name is derived from the Greek word crystals of hexahedriteOne of the main types of iron meteorites composed almost entirely of kamacite and named for its cubic (hexahedral) cleavage of α-Fe-Ni crystals. Upon etching, hexahedrites do not display a Widmanstätten pattern, but do often exhibit fine, parallel lines called Neumann lines for their discoverer, Franz Neumann, who first studied iron meteorites. They may appear also in octahedriteMost Common type of iron meteorite, composed mainly of taenite and kamacite and named for the octahedral (eight-sided) shape of the kamacite crystals. When sliced, polished and etched with an acid such as nitric acid, they display a characteristic Widmanstätten pattern. Spaces between larger kamacite and taenite plates are often iron meteorites provided the kamacite phase is about 30 mm wide. They can be seen after a polished meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and 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 bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. 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 latticeAtoms or groups of atoms repeated at regular intervals in three dimensions with the same orientation. One may regard each atom or group of atoms as occurring at a point and the resulting collection of points is the space lattice or lattice of the crystal. 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.
