Summer 1998 Gems & Gemology

VOLUME 34 NO. 2 SUMMER 1998 TABLE OF CONTENTS EDITORIAL 79 Support Your Local Researcher Alice S. Keller FEATURE ARTICLE 80 Separating Natural and Synthetic Rubies on the Basis of Trace-Element Chemistry Sam Muhlmeister, Emmanuel Fritsch, James E. Shigley, pg. 97 Bertrand Devouard, and Brendan M. Laurs NOTES AND NEW TECHNIQUES 102 Raman Investigations on Two Historical Objects from Basel Cathedral: The Reliquary Cross and Dorothy Monstrance Henry A. Hänni, Benno Schubiger, Lore Kiefert, and Sabine Häberli 114 Topaz, Aquamarine, and Other Beryls from Klein Spitzkoppe, Namibia pg. 109 Bruce Cairncross, Ian C. Campbell, and Jan Marten Huizenga REGULAR FEATURES 127 Gem Trade Lab Notes 134 Gem News 147 Thank You, Donors 148 Book Reviews 150 Gemological Abstracts pg. 115 pg. 145 ABOUT THE COVER: One of the greatest challenges for the contemporary gemologist is the separation of natural and synthetic rubies, especially when there are no characteristic internal features. A further consideration in many markets is identifying the deposit or country of origin of the ruby. The lead article in this issue reports the results of a comprehensive study on the trace-element chemistry (as determined by EDXRF analysis) of synthetic rubies from various manufacturers and natural rubies from several different deposits. The natural ruby crystal shown here on a calcite marble matrix is from Jegdalek, Afghanistan, and measures 17 x 10 x 9 mm. The accompanying 1.29 ct faceted ruby is from Mogok, Myanmar. Both are courtesy of the collection of Michael M. Scott. Photo © Harold & Erica Van Pelt––Photographers, Los Angeles, California. Color separations for Gems & Gemology are by Pacific Color, Carlsbad, California. Printing is by Fry Communications, Inc., Mechanicsburg, Pennsylvania. © 1998 Gemological Institute of America All rights reserved. ISSN 0016-626X SUPPORT YOUR LOCAL RESEARCHER ast February, many leading gemologists attended ment research institutions, the research conducted by the very successful First World Emerald Congress most gemological laboratories is not supported by out- L in Bogotá, Colombia. Of particular concern to the side funding. You are the experts on buying and selling participants was the topic of emerald treatments—that gems, so most of you know what it costs to purchase 300 is, the use of different fillers to improve the apparent one-half to one carat emeralds or rubies. In addition, even clarity of the stone. All were aware of the negative pub- though for many projects the samples do not have to be licity that emerald filling has received in recent months, large or expensive, it is critical that they be representa- and of the fact that some fillers are less effective or less tive of the particular locality, manufacturing process, or durable than others. At the Congress, representatives treatment under investigation—information that often from many of the major gemological can be provided only by members of laboratories sat together on a single the trade. As a result, researchers may panel to discuss this problem. A con- have to work for years to obtain the stant refrain from the audience, which stones for a single research project. For included dealers as well as retailers, the ruby study, some samples were was: When were the GIA Gem Trade donated, many were loaned, and oth- Laboratory, the Gübelin Gemmological ers were purchased. Our hats are off to Laboratory, SSEF, AGTA, and even all of the people who participated Gems & Gemology, among others, (more than 30 individuals and compa- going to resolve the treatment issue? nies for that study alone). Still, some dealers leave request letters unan- We, however, cannot address such swered or make promises they cannot problems without help from you in the keep, consuming precious time. Then, trade. A meaningful gemological study—whether done in when the pressure is on from consumers and the the U.S., Europe, Asia, or South America—often requires media, these same dealers want to know what’s taking large numbers of samples, hundreds of hours of testing, so long. and the participation of several experts to analyze the As the gem and jewelry industry is faced with ever-more- results. For example, the trace-element-chemistry project pressing issues regarding the disclosure of treatments and reported by Sam Muhlmeister and colleagues in this synthetics, comprehensive research will become even issue used 283 natural and synthetic rubies, from 14 more important. Knowledge gained from the scientific localities and 12 synthetics manufacturers. As Dr. Mary study of gem materials and their treatments is necessary Johnson reported at the Emerald Congress, the emerald to maintain confidence in the industry by our colleagues treatment study that GIA is currently spearheading and consumers alike. The use of broad, representative required almost 300 emerald samples, all natural, from a sets of samples, accompanied by reliable information number of known localities. Several fillers are being about the sources (or treatments) of the stones, is critical tested by various means to determine both their effective- to many of these research projects. ness and their durability under normal conditions of wear and care. So, please, think about it. And the next time you’re Often the greatest delay in conducting such a study is in asked, send some stones, provide information, share your acquiring the samples. Unlike universities or govern- experience and . support your local researcher. Alice S. Keller EDITOR Editorial GEMS & GEMOLOGY Summer 1998 79 SEPARATING NATURAL AND SYNTHETIC RUBIES ON THE BASIS OF TRACE-ELEMENT CHEMISTRY By Sam Muhlmeister, Emmanuel Fritsch, James E. Shigley, Bertrand Devouard, and Brendan M. Laurs Natural and synthetic gem rubies can be orrect gem identification is crucial to the gem and separated on the basis of their trace-element jewelry trade. However, accurate information on a chemistry as determined by energy-disper- gem’s origin rarely accompanies a stone from the sive X-ray fluorescence (EDXRF) spectrome- C mine, or follows a synthetic through the trade after it leaves try. This method is especially important for its place of manufacture. Today, natural and synthetic rubies that do not have diagnostic inclu- rubies from a variety of sources are seen routinely (figure 1). sions or growth features, since such stones Usually, careful visual observation and measurement of are difficult to identify using traditional gem testing methods. The results of this gemological properties are sufficient to make important dis- study indicate that the presence of nickel, tinctions (Schmetzer, 1986a; Hughes, 1997). In some cases, molybdenum, lanthanum, tungsten, plat- however, traditional gemological methods are not adequate; inum, lead, or bismuth proves synthetic ori- this is particularly true of rubies that are free of internal gin, but these elements were not detectable characteristics or that contain inclusions and growth fea- in most of the synthetic rubies tested. tures that are ambiguous as to their origin (Hänni, 1993; Alternatively, the concentrations of titani- Smith and Bosshart, 1993; Smith, 1996). The consequences um, vanadium, iron, and gallium––consid- of a misidentification can be in the tens of thousands, and ered together, as a trace-element “signa- even hundreds of thousands, of dollars. ture”––provide a means for separating near- Ruby is a gem variety of corundum (Al O ) that is col- ly all synthetic from natural rubies. EDXRF 2 3 ored red by trivalent chromium (Cr3+). Besides Cr, most can also help identify the geologic environ- ment in which a ruby formed, and thus rubies contain other elements in trace amounts that were imply a geographic origin. incorporated during their growth, whether in nature or in the laboratory. For the purpose of this article, we consider trace elements to be those elements other than aluminum, ABOUT THE AUTHORS oxygen, and chromium. These trace elements (such as vana- Mr. Muhlmeister ([email protected]) is research 3+ associate, and Dr. Shigley is director, at GIA dium [V] and iron [Fe]) substitute for Al in the corundum Research in Carlsbad, California. Dr. Fritsch crystal structure, or they may be present as various mineral ([email protected]) is professor of physics at inclusions (such as zirconium [Zr] in zircon) or as con- the University of Nantes, France. Dr. Devouard is assistant professor at Clermont-Ferrand stituents in fractures. The particular assemblage of trace ele- University, France. Mr. Laurs, a geologist and ments (i.e., which ones are present and their concentrations) gemologist, is senior editor of Gems & provides a distinctive chemical signature for many gem Gemology, Gemological Institute of America, Carlsbad. materials. Since the trade places little emphasis on estab- lishing the manufacturer of synthetic products, this article Please see acknowledgments at end of article. will focus on how trace-element chemistry, as determined Gems & Gemology, Vol. 34, No. 2, pp. 80 –101 by EDXRF, can be used for the basic identification of natural © 1998 Gemological Institute of America versus synthetic rubies. It will also explore how EDXRF can 80 Separating Rubies GEMS & GEMOLOGY Summer 1998 Figure 1. These six natural and synthetic rubies are typical of material that might be submitted to a gemological laboratory for identification. From top to bottom and left to right: 1.29 ct Kashan flux-grown synthetic ruby, 1.10 ct natural ruby, 0.93 ct Czoch- ralski-pulled synthetic ruby, 0.95 ct Ramaura synthetic ruby, 1.05 ct natural ruby from Tanzania, and 0.57 ct Swarovski flame-fusion synthetic ruby with flux-induced fingerprints. The 1.10 ct natural ruby was reported to have come from Mogok, but trace-element chemistry indicated that the stone was from a basalt-hosted deposit (such as Thailand); microscopy also indicated a basaltic origin. Photo © GIA and Tino Hammid. help determine the geologic origin of a natural ruby, available to gemological laboratories, or use tech- which is useful for identifying the country of origin.

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