Diamond is one of the most precious minerals in the world for its physical and optical characteristics. Due to its extremely rigid crystalline structure, it can be contaminated by few types of impurities, such as boron and nitrogen. Combined with its high transparency (corresponding to a broad band of prohibited 5.5 eV), this results in the clear and colorless appearance of most natural diamonds. Small amounts of defects or impurities (approximately one part per million) induce a blue (boron), yellow (nitrogen), brown (crystalline defects), green, violet, pink, black, orange or red diamond color. The diamond also has a relatively high refractive dispersion, that is, ability to disperse light of different colors, resulting in its characteristic luster. Its excellent optical and mechanical properties, combined with efficient marketing, make diamond the most popular gem.
