A web-like fingerprint creates a maze-like pattern in spinel.

amazing fingerprintA web-like fingerprint creates a maze-like pattern in this spinel from Vietnam, observed with darkfield and diffuse fiber-optic illumination. Photomicrograph by E. Billie Hughes; field of view 5 mm. Courtesy of Vitalit Gems.

Of the variety of inclusions that can be seen in spinel, perhaps the most familiar are angular octahedral crystals. In many cases, we even see these crystals arranged in neat rows, forming delicate “fingerprint” inclusions.

However, spinel fingerprints can also take on other appearances, as observed in a Vietnamese sample that recently passed through our laboratory (see above). This stone contained a partially healed fissure with a maze-like pattern that was evident when lit with darkfield illumination. With the addition of diffuse fiber-optic illumination, small angular areas of the channels seemed to light up with a highly reflective appearance. Myriad inclusion scenes make spinel a fascinating gem to observe.

About the Author

E. Billie Hughes visited her first gem mine (in Thailand) at age two and by age four had visited three major sapphire localities in Montana. A 2011 graduate of UCLA, she qualified as a Fellow of the Gemmological Association of Great Britain (FGA) in 2013. An award winning photographer and photomicrographer, she has won prizes in the Nikon Small World and Gem-A competitions, among others. Her writing and images have been featured in books, magazines, and online by Forbes, Vogue, National Geographic, and more. In 2019 the Accredited Gemologists Association awarded her their Gemological Research Grant. Billie is a sought-after lecturer and has spoken around the world to groups including Cartier and Van Cleef & Arpels. In 2020 Van Cleef & Arpels’ L’École School of Jewellery Arts staged exhibitions of her photomicrographs in Paris and Hong Kong.


This article first appeared in Gems & Gemology, Spring 2022, Vol. 58, No.1, p. 68.

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