Naturally Colored Yellow and Orange Gem Diamonds: The Nitrogen Factor

GEMS & GEMOLOGY SUMMER 2020 Among fancy-color diamonds, those with saturated blue, green, and red colors are the rarest and generally the most highly valued. Over the last decade, however, diamonds with pure hues in these colors have made up less than one-tenth of one percent of all diamonds examined at GIA, making them virtually unattainable in the marketplace. In recent issues of Gems & Gemology, we have documented the gemological and spectroscopic properties of the rarest of fancy-color diamonds ranging from pink-to-red, blue, and green to the more unusual white and black. This article will address the most common colored diamonds, those with yellow hues, while also examining their much rarer orange cousins (figure 1). This is the last of the fancy color groups in this series, and a brief summary of all the colored diamond groups is provided at the end of the article. Yellow and orange diamonds owe their color primarily to nitrogen impurities that are incorporated in the diamond lattice during growth deep in the earth. Nitrogen is the most common impurity in natural diamond due to the very similar atomic radii of nitrogen and carbon atoms (155 and 170 picometer Van der Waals radii, respectively) as well as the relative abundance of nitrogen in the growth environ-