Thermally stable iron oxide pigments, a process for their preparation and their use

Iron oxide pigments with an Fe(II) content of at least 5 wt. %, calculated as FeO, which have at least one inorganic after-treatment layer and at least one organic after-treatment coating, wherein the inorganic after-treatment layer consists of oxygen and/or hydroxide compounds of boron, aluminum and/or silicon and the organic after-treatment coating consists of one or more compounds of the general formula (I)

• Ar--(COOX).sub.n (I)
• wherein
• Ar represents an aromatic grouping optionally substituted with halogen, NH.sub.2, OH, NHR, NR.sub.2, OR or R, where R represents a linear or branched alkyl group with 1 to 30 carbon atoms or an optionally substituted aryl group with 6 to 10 carbon atoms;
• X represents H, an alkali metal, NR.sup.1.sub.4, where R.sup.1 .dbd.H, an alkyl or aryl group, 1/2 an alkaline earth metal, 1/3 Al or 1/3 Fe;
• and
• n is an integer from 1 to 10.