Unusual Purple Inclusion in Emerald
Depending on geographic locality, inclusions in emerald are typically similar from one stone to the next. We expect to see classic jagged three-phase inclusions in Colombian emeralds or blocky multiphase inclusions and phlogopite in Zambian emeralds, so it is always interesting for the gemologist to observe something out of the ordinary. The Carlsbad laboratory recently examined a 7.11 ct oval mixed-cut emerald (figure 1), identified by standard gemological testing. Microscopic examination revealed jagged to irregular multiphase inclusions, planes of reflective thin films, clarity-enhanced fractures, and—surprisingly—a fairly large purple inclusion with a subhedral form. Upon closer examination, distinct purple and near-colorless banding was visible (figure 2), and the inclusion proved to be singly refractive when viewed between crossed polarizers. The inclusion was too deep within the stone to confirm its identity with Raman spectroscopy, but its appearance and optic character pointed to fluorite. Based on these characteristics, another possible identity could be halite, but this inclusion strongly resembled a color-banded fluorite inclusion previously reported in emerald by GIA’s laboratory in 1969. In that example, the surface-reaching inclusion was identified by scraping a sample and analyzing it with X-ray diffraction (R.T. Liddicoat, “Developments and highlights at the Gem Trade Lab in Los Angeles,” Summer 1969 G&G, p. 63).
Fluorite inclusions in emerald have been cited from various localities, as a product of pegmatitic/hydrothermal involvement in formation (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, Vol. 3, Opinio Verlag, Basel, Switzerland, 2008, pp. 354–406; D. Schwarz et al., “Emerald and green beryl from Central Nigeria,” The Journal of Gemmology, Vol. 25, No. 2, 1996, pp. 117–141). These inclusions are usually described as colorless octahedra, although sometimes they are seen as cubes or rounded shapes. Purple banded fluorite is an unusual inclusion in emerald, making this an interesting and unexpected addition to an otherwise typical inclusion scene.
