The effect of the energy supplied (E-supp) by the planetary ball-mill on montmorillonite clay is studied. Sodium montmorillonite clay was subjected to different energies supplied, and the effects were followed by transmission electron microscopy, X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and specific surface area (BET). The results show that between 1.7 J/g <= E-supp <= 4.8 J/g, the separation, delamination, and exfoliation of the clay layers occur. At E-supp >= 6.6 J/g, the stacking of the layers is lost. At E-supp = 13.2 J/g, the maximum specific surface area is obtained. Between 26.4 J/g <= E-supp <= 38.5 J/g, a transition occurs, and the clay becomes amorphous. These results establish criteria based on the planetary ball-mill's energy to modify the montmorillonite structure optimally. (c) 2021 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.