As was noted above, the mineral composition of the cement is more useful than the oxide composition. However, the mineral composition is more difficult to determine accurately. It can be measured directly using techniques such as light microscopy, powder X-ray diffraction, or SEM X-ray analysis, or it can be calculated from the oxide composition. According to a summary by Taylor [2] powder XRD analysis is difficult because of the dominance of the C3S peaks and the extensive amount of peak overlap, and accurate results are obtained only when very careful procedures and analysis are followed. Microscopy, which involves a point-count method, tends to be operator dependent and unreliable for separating the C3A and C4AF phases