![]() Nitrogen can exist as single isolated atoms substituting for carbon (i.e., C-centers, single substitutional nitrogen, or type Ib), aggregated groupings of atoms in pairs or fours (i.e., A-centers or type IaA, and B-centers or type IaB), or as more complex defects (e.g., N3, H2, H3, H4, and NV) (figure 2 see Collins, 1997, 1999, 2001 and Breeding and Shigley, 2009 for more information). Their configuration makes a significant difference in the color. ![]() Atomic lattice defects cause different colors in diamond. While the amount of nitrogen in the earth’s mantle is significantly lower than that, about 98% of natural gem diamonds recovered (both colorless and fancy-color) are type Ia, meaning they contain FTIR-measurable concentrations of nitrogen impurities, thus proving that nitrogen is present in most diamond growth environments.įigure 2. Nitrogen is the sixth most abundant element in the universe and accounts for more than 75% of the earth’s atmosphere (Bebout et al., 2013). If nitrogen is present when diamond grows, it will inevitably be incorporated. 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 environment. Yellow and orange diamonds owe their color primarily to nitrogen impurities that are incorporated in the diamond lattice during growth deep in the earth. 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. This article will address the most common colored diamonds, those with yellow hues, while also examining their much rarer orange cousins (figure 1). 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. 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. INTRODUCTIONĪmong fancy-color diamonds, those with saturated blue, green, and red colors are the rarest and generally the most highly valued. Yellow diamonds serve as the best ambassador to the colored diamond world due to their abundance and may be the only colored diamond many people will ever see in a jewelry store. Yellow and orange diamonds can be grown in a laboratory or created by color treatments, so a thorough understanding of the defects responsible for color in the natural stones is critical for identification. With time at high temperatures deep in the earth, the nitrogen atoms in most diamonds aggregate, resulting in either near-colorless stones or yellow diamonds colored by cape defects. However, only the very rare type Ib diamonds maintain that original color. Nitrogen-bearing diamonds are thought to incorporate isolated nitrogen during growth by substitution for carbon, meaning that natural diamonds start out with yellow to orange color. ![]() Four major groups of defects are responsible for the color in nearly all yellow and orange diamonds: cape defects (N3 and associated absorptions), isolated nitrogen defects, the 480 nm visible absorption band, and H3 defects. Both categories owe their coloration to atomic-level lattice defects associated with nitrogen impurities in the diamond structure. Natural yellow gem diamonds are the most common of the fancy-color diamonds, while orange diamonds are among the rarest when they have unmodified hues. Yellow is the most common of the fancy-color diamonds, and its close relative orange is among the rarest. Applied Jewelry Professional ™ Online Diplomaįigure 1. ![]()
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