Geochemical studies were performed in clayish sedimentary rocks from Corumbataí Formation, a Paraná Basin geological unit, used as raw material for ceramic products, in order to extract information from major elements chemical analysis along with field descriptions. Through these data, variations and similarities were established among the clayish strata of three mines located in distinct municipalities of the studied region. Special attention was given to the loss on ignition, since it results mainly from the CO2 and/or water release during heating at 1000°C. The used oxides/chemical elements ratios, when plotted, show clusters and/or sequences that results from proportion, component types and weathering state of the sampled materials, which was verified by X-ray diffraction analysis. Thus fluxing effect of certain elements at temperatures greater than 1000°C was evaluated, such as sodium, which can modify the observed behavior when loss on ignition is used as the variable.
