Gem Focus August 2021: Coral

Posted on August 10, 2021 by Çiğdem Lüle, PhD, FGA, GIA GG, DGA

Coral--a sea animal revered in jewelry for thousands of years. Coral, especially the red to pink type, has been used as an ornamental gemstone both in jewelry and intricate carvings. Strangely, the word “coral” does not have an established taxonomic meaning but is instead broadly used to define for any organism that grew attached to the sea floor. In fact, gem coral is the skeletal remains of the coral polyps. It was also a confusing creature to early scientists because it possesses both animal and plant features, therefore its proper identification as an animal species was made in the 17th century, much later than many other known species. Coral, Diamond, Gold Brooch. Courtesy of Heritage Auctions. There are many species of coral that produces gem materials in different colors. While the most known and popular ones are red, black and golden coral are appreciated as even rarer types. Historically, red coral (Corallium genius) comes from the Mediterranean Sea and has been known as precious coral in traditional jewelry trade. Italy has a particular position in the market for fishing and manufacturing red coral and has for centuries. The most exquisite examples found in jewelry are from this source. Today, Japan and China are also important manufacturers of red coral, as it is fished in Asian waters too. Coral Cameo, Gold Pendant-Brooch. Courtesy of Heritage Auctions. CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) is dedicated to protecting animal and plant species survival as and when affected by international trade. Although pink to red coral from Corallium genius is traded without any restrictions, a lookalike pink coral genius called Stylaster is protected under CITES Appendix II. The reason they are very similar is that the coloring is provided by the same chemicals (carotenoids) and the mineral compounds are calcite in Corallium and aragonite in Stylaster. Since calcite and aragonite are polymorphs, it is not possible to separate them via conventional gem testing. Standard gemological testing provides means of identifying natural coral from its simulants and within different colored corals. However, in order to comply with the CITES regulations, international traders need to seek advanced testing techniques such as Raman spectroscopy to separate Corallium from Stylaster. Full disclosure and disclaimers should be provided by the sellers, regarding CITES compliance, when these items are on offer. If not, the buyer needs to be aware!

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