Patchy Yellow Trigon
Occasionally, diamonds show irregularity in their color related to heterogeneous distribution of atomic-level defects. “Yellow-skin” diamonds are evidence of this. Seen in the figure above is the rough surface of a 0.98 ct diamond that shows a trigon with patchy yellow coloration. The yellow color is caused by isolated nitrogen that is confined to the outer surface of the rough stone, making it look like the rough diamond has a “yellow skin.”
Yellow diamonds colored by isolated nitrogen are known to have uniform to patchy or irregular color zoning (more information on naturally colored yellow and orange diamonds can be found in C.M. Breeding et al., “Naturally colored yellow and orange gem diamonds: The nitrogen factor,” Summer 2020 G&G, pp. 194–219). The color zoning (or lack of) correlates with the distribution of the nitrogen in the diamond’s crystal lattice as it grows. It is theorized that the “yellow skin” is from a subsequent growth event, making it younger than the colorless diamond it surrounds.
