Gemological Institute of America (GIA) Graduate Diamonds Practice Exam

Lamellae are thin, plate-like growth zones within a crystal. When these layered zones incorporate different impurities or defects, they appear as distinct color bands along specific crystal planes. This form of internal color zoning is what colored lamellae describe—the color variation comes from the crystal’s growth history and compositional layering, not from emission of light or from electron defects that absorb or re-emit light. Color centers involve defects that create color by absorption, while fluorescence and luminescence are light-emission phenomena, which are different from the appearance of planar color layers created during crystal growth.