Oxidation-stable iron oxide pigments, process for preparing them and their use

An oxidation-stable iron oxide pigment comprising Fe(II), said FE(II) having a content of at least 5% by weight calculated as FeO;

• and
• a coating, said coating consists of an organic coating composed of one or more compounds of the general formula (I)
• R—(COOX)n (1)
• wherein
• R is a saturated or unsaturated linear or branched aliphatic radical having 1 to 15 carbon atoms which is optionally substituted one or more times by halogen and/or NH2 and/or OH and/or NHR1 and/or NR12 and/or OR1, or
• is an alicyclic or aromatic radical having 4 to 26 carbon atoms which is optionally substituted one or more times by halogen and/or NH2 and/or OH and/or NHR1 and/or NR12 and/or OR1 and/or R1,
• R1 being a saturated or unsaturated linear or branched optionally substituted aliphatic radical having in each case 1 to 10 carbon atoms or an optionally substituted alicyclic or aromatic radical having in each case 6 to 10 carbon atoms;
• X is hydrogen, alkali metal, NR24, R2 being H or a linear or branched aliphatic, alicyclic or aromatic radical, or ½ alkaline earth metal, ⅓ Al or ⅓ Fe and
• n is an integer from 1 to 10;
• wherein the iron oxide pigment has an oxidation stability in the oxidation stability test of ≧10° C. as compared with an uncoated iron oxide pigment.