Brazil’s Enigmatic Diamonds, Cuprian Liddicoatite, and Silicon in Corundum
Welcome to the first Gems & Gemology of 2017! This is an unusually diverse issue, combining Brazilian diamonds, cuprian liddicoatite tourmaline, Japanese jadeite, iris quartz, synthetic zincite, and a short but important contribution on the fundamental role of the element silicon in generating blue color in many fine sapphires.
The original geologic sources of Brazil’s most valuable diamonds remain elusive...
In our lead article, authors Darcy Svisero, James Shigley, and Robert Weldon survey Brazil’s diamond deposits. This region has produced a significant number of large rough diamonds. It’s also a source of valuable colored diamonds from predominantly alluvial deposits, but today’s diamond production is small and the original geologic sources remain mostly elusive. Although economically viable kimberlite pipes have been discovered in recent years, the outlook for increased production appears challenging.
Most researchers assume the bulk of copper-bearing tourmaline on the market today is elbaite, but some is undoubtedly another tourmaline species: liddicoatite. Yusuke Katsurada and Ziyin Sun report on the chemistry of copper-bearing liddicoatite tourmaline submitted to GIA’s Tokyo laboratory. Their study shows elevated gallium and lead content in cuprian liddicoatite, which displays stronger fluorescence under long-wave ultraviolet light than cuprian elbaite due to high concentration of rare earth elements.
In our third paper, John Emmett, Jennifer Stone-Sundberg, Yunbin Guan, and Ziyin Sun discuss the critical role of silicon in the color of gem-quality corundum. Although the effect of trace elements such as iron, titanium, and magnesium within the corundum lattice is well understood, the chemical interaction of these trace elements is not widely appreciated. The authors demonstrate that silicon’s presence is vital to the process that allows titanium to pair with iron and create blue color in sapphire. To the best of the authors’ knowledge, this topic has not been addressed in the gemological literature.
Our next paper, by Ahmadjan Abduriyim, Kazuko Saruwatari, and Yusuke Katsurada, covers the history and characteristics of Japanese jadeite and compares this highly valued gem with jadeite from other sources. Their study examines the chemical composition and chromophores of jadeite varieties from the Itoigawa and Omi regions of Niigata Prefecture and the Wakasa region of Tottori Prefecture and compares them with samples from Myanmar, Guatemala, and Russia.
Next, Xiayang Lin and Peter Heaney analyze iris quartz crystals from geodes in the Deccan Trap basalts of west-central India using scanning and transmission electron microscopy and atomic force microscopy. Their investigation reveals that certain crystal faces exhibit etching, which acts as a diffraction grating to produce iridescence.
Our final paper, by Ji Zhang, Yujie Gao, and Guanghai Shi, provides a gemological characterization of an intriguing industrial by-product: gem-quality synthetic zincite from foundries in Poland.
Be sure to investigate our three regular sections: Lab Notes documents GIA staff gemologists’ most recent findings, Micro-World reveals fascinating gemstone inclusions, and this issue’s Gem News International reports on the 2017 Tucson gem shows, including an important update on Ethiopian emerald.
We offer congratulations to the winners of our 2016 Dr. Edward J. Gübelin Most Valuable Article Award, and thank all of the readers who voted. Don’t forget to take this year’s G&G Challenge, our annual multiple-choice quiz. Thank you for all your support through 2016!