IGI certification is valuable. There are a number of different geological organizations devoted to the classification of diamonds, and the diamond industry refers to such organizations and professionals as gemologists.
IGI is an acronym for the International Gemological Institute, which is headquarted in Antwerp, Belgium. It is one of several organizations devoted to the identification of diamond attributes.
Certification in the diamond industry is a means of combating fraud. Diamonds are sold with certificates of authenticity that include their scientific attributes. The attributes of a diamond must be assessed to determine it's fair market value, and such assessment must be conducted by certified professionals. The IGI is one such organization devoted to this industry practice.