Spring 2019 G&G: Tourmaline Classification, Provenance of Freshwater Pearls, and the Annual Tucson Report
May 15, 2019
Color is king in the new issue of Gems & Gemology. From the variety of colors found in the 33 known species of tourmaline to the diverse goods seen at the Tucson gem shows, our Spring 2019 issue is a testament to the trade popularity and scientific relevance of colored gemstones. The issue also includes an article on the gemological characteristics of the Talisman of Charlemagne; provenance studies on freshwater pearls from the U.S. and China using LA-ICP-MS and LDA; the impact of cut and orientation of table facets on the color-effect in alexandrite; and a field report from the sapphire, opal, and emerald deposits of Ethiopia.
A New Method for Determining Gem Tourmaline Species by LA-ICP-MS
Gem-grade tourmaline comes in a wide variety of colors and species, from elbaite to dravite to liddicoatite. In our lead article, Ziyin Sun, Aaron C. Palke, Christopher M. Breeding, and Barbara Dutrow present a classification scheme for tourmaline that uses laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) to collect quantitative measurements of major, minor, and trace elements. These measurements allow gemological laboratories to determine tourmaline species with good precision and accuracy.
U-Pb Ages of Zircon Inclusions in Sapphires from Ratnapura and Balangoda (Sri Lanka) and Implications for Geographic Origin
Zircon is able to withstand peak temperatures but also survive post-cooling conditions. Due to these properties, when found as inclusions in sapphire, zircon is able to provide geological insight into the secondary deposits from which the host sapphires formed. A team led by Emilie Elmaleh and Susanne Theodora Schmidt investigates zircon inclusions in sapphires from two Sri Lankan deposits. Through spectroscopic methods, trace-element chemistry, and U-Pb dating the authors establish a metamorphic/metasomatic, non-basalt-related origin for these sapphires.
The Talisman of Charlemagne: New Historical and Gemological Discoveries
Housed at the Palace of Tau Museum in Reims, France, the Talisman of Charlemagne is an opulent artifact from the Middle Ages that has been said at various times to contain both hair of the Virgin Mary and pieces of the True Cross. It has been linked with Charlemagne, Napoleon, and several other historical figures. The first gemological study of the piece was recently performed at the museum with portable equipment by Gerard Panczer and his coauthors. Based on their findings and comparison with other pieces from the period, the authors were able to propose origins for the sapphire, garnets, and emeralds used in the talisman.
Provenance Discrimination of Freshwater Pearls by LA-ICP-MS and Linear Discriminant Analysis (LDA)
Some non-bead-cultured (NBC) freshwater pearls can be challenging to identify, as their growth features may be similar to those found in some naturally occurring pearls. Using LA-ICP-MS and linear discriminant analysis (LDA), Artitaya Homkrajae, Ziyin Sun, Troy Blodgett, and Chunhui Zhou were able to pinpoint a method that identifies the growth environment of freshwater pearls with greater confidence.
Pleochroism and Color Change in Faceted Alexandrite: Influence of Cut and Sample Orientation
The color appearance of faceted alexandrites results in large part from the gem’s pleochroism, but it may also be influenced by trace-element content, cut, size, and other factors. Using samples cut from synthetic crystals, Karl Schmetzer investigates the color appearance of faceted alexandrite. He documents the impact of the inevitable multiple internal reflections on placement of this biaxial gem’s table facet, as well as its perceived color change and pleochroism.
Land of Origins: A Gemological Expedition to Ethiopia
In the past decade, Ethiopia has become known as a source of opal, sapphire, and emerald. In 2018, a field expedition led by Wim Vertriest explored the various gem deposits of Ethiopia. While there, the team visited mines and markets, documented methods of mining, and experienced the cultures of the different regions of this remarkable country.
Notable examinations by GIA laboratory staff around the world include the largest diamond ever mined in North America, a color-change sapphire from Myanmar (formerly Burma), and the largest gahnospinel seen by GIA.
Diamonds from the Deep
In our newest section, Karen Smit and Steven Shirey explore the ages of natural diamonds and the impact they have on the world around us. They discuss how diamond formation is linked to plate tectonic processes, as well as how elements are recycled in the deep earth.
G&G’s section on inclusions and photomicrography highlights grandidierite inclusions in sapphires, a fossil insect in a free-form opal, and copper inclusions in a purple chalcedony from Indonesia.
Gem News International
Our annual Tucson report features colored stone market trends, the work of designers such as Derek Katzenbach and Paula Crevoshay, and trade involvement in the responsible sourcing of gemstones [link here to “Sourcing Stones with Columbia Gem House”]. Non-Tucson Gem News entries focus on sapphires [link here to “Sapphires from Colombia”] and trapiche emerald [link here to “Trapiche emerald from Colombia”], both from Colombia, and CIBJO’s new responsible sourcing Blue Book.
The Spring issue also contains the 2017 Gems & Gemology Challenge. Score 75% or better and you’ll receive a certificate of completion (PDF file); earn a perfect score and your name will be listed in the Fall 2019 issue. Mail-in cards and online entries for the Challenge must be submitted by Monday, August 12, 2019.
Jennifer-Lynn Archuleta is the editor of Gems & Gemology.