Magnetite crystals with unique morphological characteristics have been grown from hematite under hydrothermal conditions at 150 and 175 degrees C in the presence of hydrazine and copper (II) oxide. In the absence of CuO, octahedral crystals of magnetite with a distribution of particle sizes were grown in accordance with literature procedures. In the presence of CuO, magnetite crystals with distorted morphology were prepared in which the [111] crystal faces were absent, leaving a framework structure of corners and edges. Examples of crystal intergrowths were observed, as well as the partial collapse of the framework structure of the magnetite. The results are discussed with reference to the possible effect of copper redox couples on the hematite reduction reaction.