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

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. Diamonds with euhedral crystals displaying vibrant color are particularly rare.

A grader in GIA's New York Laboratory recently observed just such features in a 1.01 ct, F-color, round brilliant diamond with perfectly formed bluish green and reddish orange crystal inclusions (figure 1). In light of the upcoming holiday season, the grader fondly referred to it as the "Christmas" stone due to the combination of colors.

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

Although Gems & Gemology has documented such eclogitic inclusions before, this inclusion scene was unusual because of the proximity of the crystals to each other and the vibrancy of their colors. Also interesting was the discovery that both crystals had formed within the same growth sector, as can be seen from the DiamondView^TM image in figure 2, which distinctly illustrates an octahedral growth zone surrounding the inclusions. Using Raman analysis (830 nm laser), staff members identified the reddish orange crystal as Fe-rich garnet and the bluish green crystal as omphacite (a pyroxene).

These inclusions are an excellent example of well-formed syngenetic crystals in diamond. In this case, they were also the features that led to an SI₂ clarity grade, a somewhat disappointing result given the diamond's unique beauty and character. GIA diamond graders view thousands of stones annually, and it is refreshing to see an attractive grouping of inclusions that readily tell a story of the diamond's journey to the present.

Bonny S. Alphonso, Jennifer Schahn, and Paul Johnson
GIA Laboratory, New York