The cordierite is commonly prepared by reaction of talc, clay and gibbsite within the range of 1200-1350degreesC. This study deals with the effect of the amorphization by grinding of that mixture and its influence on the cordierite formation.The mixture previously mentioned underwent six different treatments: mixing without grinding (A) (only mixing); non-amorphizing grinding (Am) and amorphizing grinding in oscillating mill at four different times (H samples). The phases formed by thermal treatment were studied using differential thermal analysis (DTA)-thermogravimetric analysis (TG)-DTG, dilatometries and X-ray diffraction (XRD) techniques in certain combinations.The thermal analysis of the A and AM series were compared and they do not show significant differences, whereas the H samples present remarkable alterations in the DTA peaks as well as in the weight losses (TG). Thus, a great number of DTA peaks tend to decrease the temperature of the maximum and to lower the intensity as the amorphization time increases.Calcination tests performed within the range 900-1200degreesC show important differences in the diffractograms obtained from the intermediate products. While at 1350degreesC the A and H samples reach the same final phases, within the range 1200-1360degreesC they present important differences in the DTA indicating that the sequence and direction of reaction are different. The same behavior can be observed by dilatometric analysis. (C) 2003 Elsevier B.V. All rights reserved.