Octahedral Gahnospinel Crystal in Sri Lankan Blue Sapphire
A greenish blue octahedral crystal of gahnospinel found in Sri Lankan blue sapphire. Photomicrograph by Yusuke Takamura; field of view 3.81 mm.
Recently, the authors encountered a greenish blue octahedral crystal inclusion in a Sri Lankan blue sapphire (see above). Visual features, such as the greenish blue color and octahedral shape, and Raman spectroscopy identified the inclusion as gahnospinel, with the formula (Mg,Zn)Al2O4.
Gahnospinel inclusions in sapphire often suggest a Sri Lankan origin (A.C. Palke et al., “Geographic origin determination of blue sapphire,” Winter 2019 G&G, pp. 536–579). In addition, gahnospinel inclusions with euhedral crystal shape have been reported previously (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, Volume 3, Opinio Verlag, Basel, Switzerland, 2008). This crystal, however, shows large and beautiful octahedral features.
