Internal Structures of Natural Pearls from Pinctada maxima, Identification of Resin-Filled Turquoise, Spinel Inclusions Chart, and More……
Spring ushers in a feeling of renewal, and as we start to slowly recover from the global pandemic, it is a welcome sentiment. Join us as we investigate the inner structures of natural Pinctada maxima pearls, the technical evolution of turquoise treatments using resin filling, and a mathematical approach to predicting color in uniaxial gemstones. Even though the Tucson gem shows were canceled this February, we are able to offer more than 20 pages of captivating interviews covering how many in the trade have been weathering the situation along the entire supply chain.
“A mathematical method using visible spectroscopy to accurately predict color, the most important quality for a colored gemstone…”
Natural Pinctada maxima pearls take center stage in the lead article as Artitaya Homkrajae and fellow GIA researchers conduct a detailed analysis of 774 natural pearls collected from wild marine mollusks. These pearls were classified into six broad internal structural types based on X-ray techniques such as real-time microradiography (RTX) and X-ray computed microtomography (μ-CT). The results of this work support the efforts to aid in the dependable identification of natural versus cultured pearls by gemological laboratories.
In the second article, Ling Liu and a team from the Gemmological Institute, China University of Geosciences in Wuhan use ultraviolet fluorescence, spectrofluorometry, and Fourier-transform infrared (FTIR) spectrometry to characterize resin-filled turquoise. Their research addresses an urgent need to detect the prevalence and constantly evolving treatment techniques applied to turquoise sourced from China’s Hubei Province.
Next, Che Shen and coauthors provide a mathematical method using visible spectroscopy to accurately predict color, the most important quality for a colored gemstone, and guidance on cutting backed by science. This comprehensive study predicts the color of a uniaxial gem when viewed in any direction by reconstructing unpolarized spectra provided the polarized spectra and relative viewing angle to the c-axis are known.
In our last article, Nathan Renfro and coauthors present a beautiful array of inclusions in natural, treated, and synthetic spinel, as well as inclusions of spinel in other gemstones. Their colorful spinel inclusions chart is enclosed with every printed copy of this issue. Laminated versions of it, along with the five inclusion charts, are also available at store.gia.edu.
As always, interesting gemological findings abound in our regular sections. Discover natural diamonds displaying asterism and bicolor rough diamond crystals featuring distinct colorless and pink areas in Lab Notes, while Micro-World delights with a glimpse into the inner landscapes of gems: a kaleidoscopic play of interference colors seen in thin-film fluid inclusions in aquamarine and a cloud inclusion shaped like a diamond profile mimicking its diamond host. The Gem News International section features a virtual report on the pandemic’s impact and how the trade adapted their business practices to continue to flourish, as well as the headline-grabbing Cookie Monster geode and a glance back in time at hand-drilled holes in diamond briolettes. This issue also contains the annual G&G Challenge, where you can test your gemological knowledge of our 2020 issues. Finally, be sure to see our announcement of the Dr. Edward J. Gübelin Most Valuable Article Award winners.
We hope you enjoy the Spring 2021 edition of Gems & Gemology!
Duncan Pay | Editor-in-Chief | dpay@gia.edu
