Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 13. 1987. (Budapest, 1987)
characterized by an endothermal peak on the DTA-curve, while the DTG curve shows weight loss. There is a continuous transition between the endothermal water loss peak and the exothermal organic matter peak; the boundary has been designated at the equilibrium point of the DTG curve and at the crossing of the DTA curve and the base line passing from the endothermal to the exothermal peak. This transition was positioned generally between 200-240°C; we have designated the first boundary here. Fig. 8 Mean pH of A, B and C levels in the profiles 2. The oxidation province of organic matter spreads from ca. 200-240 C to about the endothermal peak of clay mineral, starting from about 500°C. This province is covered by a composite exothermal peak, assigned to the oxidation of organic matter. However, this is not always true, as this province contains the provinces of water loss of iron-oxide, ironoxide-hydroxide, and silica colloids, and oxidation of Fe (II). The latter ones are covered by the organic peak, consequently we had to include all these peaks into the weight loss of organic matter. However, it does not affect our results significantly. The DTA peak of organic matter can be divided into several sub-peaks, assigned to differently humified organic matter of various origin (humus, coarser root and chitin remnants). The question has arisen, whether it i3 not pyrite that causes the frequently double exothermal peak. To solve this problem a lead-acetate probe was applied (following the method of ERDEY 1970). The sample was heated in concentrated HCl in a test-tube. The HCl releases the sulphur content of the sample as H 2 S. The ascending H 2 S makes the lead-acetate soaked filter-paper on the mouth of the test-tube black, since the lead-acetate reacts with HgS and forms black precipitate. This reaction is very sensitive and can prove the presence of 10"" g H n S. This method was applied to all samples suspected to contain pyrite, but all results were negative.
