Winter 2019 G&G: Geographic Origin Special Issue
January 31, 2020
The Winter 2019 edition of Gems & Gemology is devoted to the determination of geographic origin for specific colored gemstones. This issue hopes to promote a healthy discussion about this complex subject, and bring greater transparency on the testing methods and criteria utilized in GIA’s laboratories.
The Geographic Origin Dilemma
Shane McClure and co-authors introduce the many facets of geographic origin determination. The authors explain that in order to adequately issue geographic origin reports, a laboratory must meet three requirements: scientific instrumentation, experienced gemologists, and a comprehensive collection of reference samples of known provenance.
Geology of Corundum and Emerald Gem Deposits: A Review
Similar geologic environments can produce gems with similar gemological properties, making it difficult to connect the properties of individual gems to the geology of their deposits. Gaston Giuliani and Lee Groat review the classification systems of corundum and emerald deposits, and discuss how genetic models can give geologic and geographic clues on their origins.
Field Gemology: Building a Research Collection and Understanding the Development of Gem Deposits
Wim Vertriest, Aaron Palke, and Nathan Renfro discuss the importance of building a reliable reference collection of known provenance in order to support geographic origin determination. Since gem-producing areas are constantly changing, field gemologists play a critical role in documenting the global mining and trading environment and the development of gemstone enhancement procedures.
A Review of Analytical Methods Used in Geographic Origin Determination of Gemstones
Origin determination is possible because there is a close relationship between the geology of an area and the properties of gemstones found there. Groat and co-authors take an in-depth look at the analytical techniques commonly used to characterize gemstones.
Geographic Origin of Specific Gemstones
In some cases, the value of a gemstone depends strongly on its geographic origin. Careful analysis of inclusions, trace element chemistry, and spectroscopic data often lead to conclusive origin determination. However, there are instances where the overlap in data is too great and laboratories are unable to make the call. Each article in this series—blue sapphire, ruby, emerald, Paraíba tourmaline, and alexandrite—outlines GIA’s methods and criteria for establishing geographic origin of that particular gemstone.
What does the future hold for the geographic origin service? Could non-industry instrumentation and techniques be adapted to gemstone applications in order to improve consistency? McClure and co-authors explore whether developing a service for additional gemstones carries enough value to justify the expense.
Brooke Goedert is associate editor of Gems & Gemology at GIA in Carlsbad, California.