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Abstract  

In the present paper the thermal behaviour of Mg-carbonates and -silicates is reviewed and discussed, based on own DTA investigations and data from the literature. Mg-bearing minerals in soils and sediments offer informations about the palaeoenvironment and palaeoclimatology of sediments and soils and - thus - the study of their crystal chemical compositions by means of (differential) thermal analysis informs about environmental conditions of (sedimentary Mg-) mineral (trans-) formations. The paper stresses (1) the interrelations between decomposition temperatures of (Mg-) carbonates and substitution processes and is (2) concerned with the interdependence between the dehydroxylation behaviour of Mg-bearing sheet silicates and their crystal chemical composition.

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Abstract  

The comparison of thermal stabilities of different organoclay intercalation complexes is presented in this work. Montmorillonite/monomer and montmorillonite/polymer intercalation complexes with similar basal spacings show a pronounced difference in changes of d 001 values after 30 min heating. The hydrophilic and/or organophilic surface modification of the starting montmorillonite is an important factor affecting the intercalated amount of organic material and thus the expansion of the sheet silicate structure.

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Abstract  

Traditional black pottery produced in Nádudvar, E-Hungary, was studied by 57Fe Mössbauer spectroscopy, X-ray diffractometry and microscopy. Quartz, feldspar, clay minerals (kaolinite, smeetite, illite) and calcite were identified in the basic clay material by X-ray diffractometry (XRD). Mössbauer spectroscopy (MS) of the original clay revealed that about 35% of iron compounds were present in goethite while the rest in clay minerals (illite and smectite). After firing the clay in air using an electric furnace (red pottery is prepared in the same way), the Mössbauer spectra showed hematite as the only iron oxide or hydroxide phase, being in good agreement with X-ray diffractometry. In the black product itself, fired in the traditional open-flame furnace, the Mössbauer spectra reflected the presence of iron in magnetite and in sheet silicates with approximately the same relative ratio of oxides and silicates as in the starting material. This can be interpreted as a result of the transformation of goethite to hematite in the first step of firing (in air), and as a reduction of hematite to magnetite in the second step of firing (closed from air). A significant difference was found in the distribution of iron at the Fe2+ and Fe3+ cation sites in the black surface (more Fe2+) and at the dark gray bulk of the fired pottery (less Fe2+), showing that the reduction of Fe3+ occurs in the silicates instead of further reduction of the magnetite (e.g., to wüstite).

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can be bound as an oxide in minerals and it can also be found in amorphous state. The morphology of sample A is angular, crystalline of the mica group of sheet silicate minerals as a TEM study has shown in Fig. 3a . The leading use of dry

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