The fundamental use of the microscope in Portland cement clinker analysis is to bring to the observer a visual appreciation of phase identities, sizes, conditions, and mutual relationships. With only a basic assemblage of equipment, microscopical analysis can be easily performed, in many cases within a few minutes. The rapidity with which potentially energy-saving information can be acquired clearly renders the analysis economically justifiable, especially in routine quality control and troubleshooting situations. In addition, the microscope has obvious value in scientific research in the manufacturing process.