| Sumario: | A set of clays from several sedimentary beds belonging to the Tertiary period (mainly Miocene) and located on the right bank of the Guadalquivir River, from Peñaflor on the northeast to Benacazón and Pilas on the southwest and interesting from the ceramic viewpoint, has been studied. The following techniques have been used: chemical, mechanical and ponderal thermal analysis, D.T.A., base exchange capacity, X-ray diffraction analysis, electron microscopy, plasticity water, plasticity, drying shrinkage at 50ºC (Boufry's diagrams), firing shrinkage and crushing strength in fired bodies. It is concluded that the main component of these clays is montmorillonite, followed by a high percentage of illites in an advanced stage of transformation to montmorillonoids. Moreover, they also contain little to important amounts of kaolinite, free silica and calcite, followed by different amounts of hydroxides. The natural samples contain about 30-40 % of fine-grain calcite. The technological tests bear out the fact that some of these materials had been used for centuries by the traditional pottery industry of Seville, for their good ceramic properties.
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