PURPOSE: To improve dispersibility, workability, heat resistance and blackness by heating magnetite particles coated with Mn and Fe compound at a prescribed temperature to provide a hematite structure consisting essentially of iron in which Mn is subjected to solid solution.

CONSTITUTION: An aqueous solution of iron (II) salt is reacted with an aqueous solution of alkali hydroxide of 1.01-1.3 equivalent weight based on Fe2+ in the aqueous solution of iron (II) salt to afford a suspension containing an iron (II) hydroxide colloid. Oxygen-containing gas is introduced into the suspension while heating the suspension to 45-100°C to prepare a suspension containing magnetite particles. Then Mn or Mn and Fe2+ are added in a state of aqueous solution to the suspension and the mixture is heated and oxidized to apply a Mn compound, Fe compound, etc., to magnetite particle surface. Then the particles are filtered and burned at 750-1000°C. Thereby particles consisting essentially of iron in which Mn is subjected to solid solution, having hematite structure and having 0.2-0.8μm diameter are obtained.