Influence of dolomite microcrystals on the technological properties of Santa Cruz de Mudela clays used for building ceramics

This study is focused on the anomalously high plasticity of Santa Cruz de Mudela clays, traditionally used for the industrial production of bricks and roof tiles. Such a high plasticity makes necessary to add degreaser material to the ceramic paste despite they have very high carbonate content. These materials have been characterised both mineralogically and technologically to their optimum industrial utilisation. They are mainly composed of phyllosilicates (illite, kaolinite, smectite and palygorskite) and quartz with high dolomite content that is a contradiction to the high plasticity. Images of scanning electronic microscopy (SEM) reveal dolomite crystals with grain sizes of 2 μm, explaining the high plasticity of these materials. Very small dolomite grains could improve the distribution during mixing process as well as the reaction between both CaO and MgO produced from clay minerals during the firing process.