A suitable external standard method which was first described by O’Connor and Raven (1988) (“Application of the Rietveld refinement procedure in assaying powdered mixtures,” Powder Diffr. 3, 2–6) was used to determine the quantitative phase composition of a commonly used Ordinary Portland Cement (OPC). The method was also applied in order to determine amorphous contents in OPC. Also investigated were the impact of atomic displacement parameters and the microstrain on the calculated amorphous content. The investigations yielded evidence that said parameters do indeed exert an influence on the calculated amorphous content. On the basis of the data produced we can conclude that the method used is entirely to be recommended for the examination of OPC. No significant amorphous content could be proven in the OPC used.