Mineral inclusions are very useful when identifying diamond, as well as in determining its origin of color and basic geology. Often, they are also the determining factor in setting the clarity grade. Unusual inclusion arrangements can be a pleasure to observe and can enhance interest in the stone when the internal feature resembles a heart or other familiar object. However, diamonds with euhedral crystals displaying vibrant color are exceedingly rare.

Recently, a grader in the New York lab observed just such features in a 1.01 ct, F-color, round brilliant diamond with well-formed bluish green and reddish orange crystal inclusions. In light of the upcoming holiday season, the grader fondly referred to the find as the “Christmas stone” due to its combination of colors.

Figure 1. A 1.01 ct diamond revealed these distinctive reddish orange garnet and bluish green omphacite crystals. Photomicrograph by Jason Darley, magnified 100x.

Although we have documented such eclogitic inclusions before (see, e.g., Spring 2002 Lab Notes, pp. 80–81; W. Wang et al., “Natural type Ia diamond with green-yellow color due to Ni-related defects,” Fall 2007 Gems & Gemology, pp. 240–243), this inclusion scene was unusual because of the proximity of the crystals to each other and the vibrancy of their colors (figure 1). Also interesting was the discovery that both crystals had formed within the same growth sector, as can be seen from the DiamondView image in figure 2, which distinctly illustrates an octahedral growth zone surrounding the inclusions. Using Raman analysis (830 nm laser), we identified the reddish orange crystal as almandine-rich garnet and the bluish green crystal as omphacite (a pyroxene).

Figure 2. This DiamondView image shows that the crystals in figure 1 were trapped with a second omphacite crystal within a single octahedral growth sector.

Bonny S. Alphonso, Jennifer Schahn, and Paul Johnson