Abstract
Polarized infrared absorption and reflection spectra along the a-, b- and c-axis directions on single crystals of K feldspar were measured and the obtained bands were assigned. The normal coordinate treatment was made on a modified Urey-Bradley force field, and the determined force constants explain well the observed frequencies. The vibrational modes were obtained from the determined force constants and the broadening and displacement of peaks with increasing disorder of Al/Si distribution was theoretically explained by these vibrational modes.