We report on the reconstructions induced by the segregation of contaminants at the (001) surface of Fe3O4(magnetite). Natural and artificial single crystals of magnetite were annealed in ultra high vacuum (UHV) at ∼ 1000 K for periods of time ranging from few hours to several days. This preparation procedure causes impurities to segregate to the surface. Analytical techniques such as Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) were used to study this effect. From previous studies we have determined that a clean surface of magnetite exhibits a (&sqrt2; × &sqrt2;)R45° reconstruction and, following our preparation procedure, is terminated at the octahedral plane. As impurities (K and Ca) segregate to the surface, the onset of a p(1 × 3) reconstruction was observed by LEED. As the annealing time increased, it was determined by AES that only Ca contaminants were present on the surface leading to a p(1 × 4) surface reconstruction. We propose two models to explain the observed p(1 × 3) and p(1 ×4) reconstructions which are in agreement with our AES, LEED and STM results. © 2003 American Institute of Physics