宝石ニュース·インターナショナル Gems & Gemology, Fall 2013, Vol. 49, No. 3

Unusual Dumbbell-Like Inclusion in Diamond


Figure 4. This 0.40 ct round brilliant diamond displayed a large, unusually shaped inclusion. Photo by Aurélien Delaunay.
When mineral-rich fluids become trapped in open cracks and evaporate, they can leave behind epigenetic mineral precipitates. These epigenetic mineral deposits are fairly common in gem materials, usually taking the form of brownish iron oxide staining in cracks. These deposits are often a nuisance, impairing the potential beauty of the finished gem, but occasionally they contribute vibrant colors with interesting geometric shapes, such as inclusions of pyrite trapped in cracks in quartz.

Figure 5. At first inspection, this dumbbell shape was reminiscent of the metallic flux inclusions seen in HPHT synthetic diamond. Photomicrograph by Aurélien Delaunay; magnified 120×.
An unusual freeform cabochon of rock crystal quartz (figure 1), obtained from Leonardo Silva Souto (Cosmos Gems, Teófilo Otoni, Brazil) and reportedly of Brazilian origin, was examined at GIA’s Carlsbad laboratory. The 52.99 ct stone contained several interesting inclusions of malachite (figure 2). These inclusions were obviously epigenetic, as they were confined within secondary cracks in the quartz host. This planar confinement caused the inclusions to grow outward after nucleating. The flattened discs were particularly interesting due to the vibrant interference colors visible in polarized light (figure 3), as well as their uniform structure. The identification of the inclusions and the host was confirmed by Raman spectroscopy.

Figure 6. DiamondView luminescence images demonstrated the diamond’s natural origin, as only traces of octahedral growth were found. The inclusion is crystallographically oriented, parallel to the edge between two octahedral faces, as highlighted by the slightly more inert elongated rectangle beside it. Photomicrograph by Aurélien Delaunay, magnified approximately 60×.
Malachite has been previously reported as a syngenetic inclusion in chalcedony and gypsum (e.g., E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, ABC Edition, Zurich, 1986), but epigenetic malachite in quartz is rather uncommon. In this stone, the resulting vivid green color is an improvement over the otherwise ordinary, colorless quartz.

Emmanuel Fritsch is a researcher at the Institut des Matériaux Jean Rouxel (IMN), University of Nantes, France; and Aurélien Delaunay is a researcher at the French Gemmological Laboratory in Paris.