The structural evolution with annealing time at 1150 degrees C of pure cordierite and of highly K-doped cordierites (KxMg2Al4+xSi5-xO18, 0.25 less than or equal to x less than or equal to 1) has been studied by means of powder X-ray diffraction and Infrared spectroscopy. The continuous orthorhombic distortion observed has been evidenced by (i) the broadening of the characteristic 211 hexagonal X-ray diffraction peak (ii) noticeable splittings of some vibrational bands related to the removal of degeneracy during the hexagonal ---> orthorhombic transformation. It is all the less important since the K-content is high. In the first times of annealing the orthorhombic distortion is accelerated for K-doped cordierites with respect to pure cordierite.