Structural signs of impact deformation of the Sikhote Alin iron meteorite

Optical microscopy, transmission electron microscopy, and electron diffract ion were used to study the structural state of a coarse (type IIB) Sikhote Alin octahedrite. During its destruction in the atmosphere and after fallin g to the Earth, the Sikhote Alin meteorite underwent an impact. Traces of d eformation such as uniformly distributed dislocations, dislocation loops, c ellular dislocation substructure, Neumann bands, deformation microtwins, lo calized shear bands, fine fragmented structure, serrated boundaries of micr ofragments, broken branching dislocation boundaries, and microcracks were f ound in the meteorite microstructure. The formation of these defects in the meteorite samples depends on the intensity of impact action. No traces of the reversible alpha --> epsilon --> alpha phase transformation were found in the microstructure of the meteorite samples. Upon the shock loading duri ng the fall, the pressure affecting the Sikhote Alin meteorite did not exce ed 12 GPa. The degree of true local deformation could reach 4-5. Fine oxide and hydroxide precipitates caused by the oxidizing action of atmosphere du ring a long period of the meteorite exposure at the Earth surface were foun d in the surface layers of the meteorite material.