Recent applications of Scanning Electron MicroscopeCathodo Luminescene (SEM-CL) technique in petrology are summarized. Observations of quartz using CL detectors attached to SEM with high magnification and resolution have shown various microstructures, such as dark streaks, patches, healed fractures, zoning, shears, planar features, etc., which are invisible under traditional petrographic microcopes. These microstructures are diagnostic for detrital quartz of different origins. Quartz in hydrothermal and magmatic rocks reveals penetration, recrystalization and dissolution textures, indicating multi-generation growths and modifications and physicochemical conditions under which they are formed. Therefore, the new technique applies to studies of sedimentary provenance, petrogenesis, and magmatic and mineralization processes.