The mechanochemical activation (dry grinding) causes destruction in the crystal structure of kaolinite by the rupture of the O-H, Al-OH, Al-O-Si, and Si-O bonds. The major mineral constituents of natural kaolins are kaolinite and quartz. In this study, the attention was mainly directed to the role of quartz content (4, 25, 50, and 75 wt%) in the mechanochemical amorphization of kaolinite. Grinding experiments were carried out for 1, 2, 3, and 4 h in a planetary mill. The rate of destruction of the kaolinite structure was followed by X-ray diffraction, thermal analysis, and Fourier transform infrared (DRIFT) spectrometry. The distortion and rupture of the kaolinite structure induced by grinding was reflected in line broadening, increases in mean lattice strain, and reduction of peak areas (intensities). The increased quartz content resulted in acceleration of the mechanically induced amorphization of the kaolinite structure. The crystalline order of kaolinite was completely destroyed after grinding the sample containing 75 wt% quartz for 4 h. On the other hand, 4 h of grinding was sufficient only to cause some increase in the defect density of kaolinite in the case of samples with lower quartz contents (25 and 4 wt%). The results indicate that quartz grains act as grinding bodies during the intensive dry grinding of kaolinite.