Carlsbad, Calif. – Aug. 18, 2005 – The Gemological Institute of America (GIA) has released the Summer 2005 edition of its award-winning quarterly journal, Gems & Gemology. This issue features a definitive study of natural-color yellow diamonds, plus reviews of emeralds from the Kafubu area of Zambia and tourmaline from the historic deposits at Mt. Mica, Maine.
While yellow diamonds are the most common of the "fancy-color" diamonds, relatively little has been published on their color appearance and grading. In the lead article, "Characterization and Grading of Natural-Color Yellow Diamonds," colored diamond expert John King and a team of GIA colleagues present data on more than 24,000 samples examined by the GIA Laboratory during the years 1998 and 2003. This research documents for the first time five subgroups of yellow diamonds with distinct spectroscopic properties. Also included is a tone and saturation chart that illustrates the color appearances of yellow diamonds, plus a discussion of the critical role cut plays in determining the final color grade of the diamond.
"Natural-color yellow diamonds command attention because they occur in large sizes and in some of the highest levels of saturation seen in colored diamonds," said Alice Keller, editor-in-chief of Gems & Gemology. "This article provides a better understanding of the properties of yellow diamonds and the different factors that must be taken into consideration during color grading. It's an important follow-up to John King's previous G&G features on blue diamonds [Winter 1998] and pink diamonds [Summer 2002]."
Zambia is considered the world's second-most important source of fine-quality emerald, after Colombia. In "Emeralds from the Kafubu Area, Zambia," Dr. J. C. Zwaan and co-authors examine these gems and their associated deposits. The article concludes that although many of their features are comparable to those of emeralds from other localities, Zambian emeralds can usually be separated by a combination of their physical properties, microscopic characteristics, and chemical composition.
The first discovery of gem tourmaline in the U.S. was at the famed Mt. Mica deposit in south-western Maine, where production began more than 180 years ago. Although mining was sporadic for several decades, recent activity has yielded gem- and specimen-quality tourmaline in a variety of attractive colours. In "Mt. Mica: A Renaissance in Maine's Gem Tourmaline Production," Dr. William B. Simmons and co-authors explore the gemmological properties and chemical composition of these gems, with a look at the locality's geology and mining history.
Rounding out the issue are G&G's regular Lab Notes and Gem News International sections, which deliver incisive coverage of the latest developments in gemmology. The Lab Notes section includes the GIA Laboratory's examination of two unusual fracture-filled diamonds and its investigation of treated-color "golden" freshwater cultured pearls. Gem News International reports on a range of unusual inclusions, new sources of Kenyan ruby and pink sapphire, Pakistani demantoid garnet, and more.
About GIA: An independent nonprofit organization, the Gemological Institute of America (GIA) is recognized as the world's foremost authority in gemology. Established in 1931, GIA has translated its expert knowledge into the most respected gemological education available. In 1953, the Institute created the International Diamond Grading System™ which, today, is recognized by virtually every professional jeweler in the world. Through research, education, gemological laboratory services, and instrument development, the Institute is dedicated to ensuring the public trust in gems and jewelry by upholding the highest standards of integrity, academics, science, and professionalism.
Image: [The Summer 2005 issue of Gems & Gemology features a definitive study of natural-color yellow diamonds.]. Photo © 2005 Gemological Institute of America. Reprinted by permission.
22nd August 2005