Microscopical methods for quantitative determination of phase percentage in rocks, bricks, portland cement clinkers, and other composite materials, although time consuming, are among the most reliable techniques available. For particle mounts on glass microscope slides, the line, ribbon, or Fleet methods are used. For thin sections or polished sections, the linear traverse or point-counting methods are recommended. Microscopically determined percentages can obviously include crystalline and amorphous phases, which is more than X-ray diffraction can clearly reveal. Microscopical data can be converted into oxides, giving a chemical analysis. The gathering of microscopical data is facilitated by electronic tallying devices and semiautomatic mechanical stages. Finally, microscopical data, properly gathered, can be treated statistically with high levels of confidence. One should be aware, however, of the limits that each microscopical method entails.