This paper addresses the application of thermal analytical methods (DTA/DSC/TG/ MS) in soil investigations, especially the interrelation of exothermic effects and analytical or preparative parameters. For the superimposed decomposition/ oxidation reactions of siderites, FeCO3, the heating rate is shown to have a decisive influence because low heating rates tend to suppress the endothermic effect. In mixtures of small amounts of organic matter (glucose and starch) with talc, the phyllosilicate acts as a catalyst by influencing the intensity of combustion of the organic matter.