The products of Cr-smectite clays heated to 1350 °C in nitrogen were evaluated by X-ray diffraction and chemical analysis. Cr-smectite clays were prepared at room temperature by contact between smectite clays and Cr species contained in OH-Cr solutions. The Cr species were prepared using chromium nitrate solution by addition of NaOH solution with OH/Cr = 2. Products of firing in nitrogen at the high temperature were different (magnesia chromite, donathite, iron chromium oxide and picrochromite) depending on the type of isomorphous substitution of the smectite structure and the amount of retained chromium.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - (CETMIC)