AbstractThe differential thermal method, by determining the thermal reactions undergone by a clay or shale, is a rapid means of identifying the mineral components of such materials, and because the properties of clays and shales depend largely on their mineral composition, it is at the same time a rapid method of evaluating the properties of such materials.Differential thermal analyses are presented for the pure forms and synthetic mixtures of the common components of clays and shales, namely, kaolinite, halloysite, illite, montmorillonite, quartz, gibbsite, boehmite, diaspore, dolomite, calcite, gypsum, organic material, pyrite, marcasite, goethite, and limonite.Differential thermal analyses are presented also for a variety of well‐known types of clays, and on the basis of the thermal data for the pure components, the mineral composition is indicated. The correlation of mineral composition of clays and shales (as reflected in the differential thermal curves) with the ceramic properties is discussed as a basis for using this thermal method to indicate the properties of such materials.Finally, differential thermal analyses are presented for sequences of samples from the pits of several operating clay products plants in order to illustrate the way in which the method can be applied in prospecting and in plant control.