The thermogravimetric method offers a new approach to the study of clay and clay-like minerals as well as other minerals and compounds that gain or lose weight upon heating. This method is complementary to differential thermal analysis, which records energy gains or losses upon heating. Thermogravimetric curves for clay and clay-like minerals are presented and correlated with curves obtained by the differential thermal method. The apparatus, procedures, limitations, and application of the method are described and illustrated.