THE BIRON HYDROTHERMAL SYNTHETIC EMERALD by Robert E

THE BIRON HYDROTHERMAL SYNTHETIC EMERALD By Robert E. Kane and Richard T. Liddicoat, ]r. A new synthetic emerald grown in Western merald was first synthesized by Ebelman in 1848 by Australia is now commercially available E adding natural emerald powder to a molten boric acid as faceted stones. Infrared spectra revealed flux, which produced very small prismatic emerald crys- the presence of water, thereby confirming tals as the mixture cooled. In the ensuing years, the flux that these synthetic emeralds are synthe- growth of synthetic emerald was achieved by many re- sized by a hydrothermal process. Chemical searchers (Nassau, 1980; Sinkankas, 198 1). In 1957, the analysis showed that they contain vanadium as well as lesser amounts of chro- growth of minute beryl crystals by a hydrothermal process mium. This new synthetic exhibits some was first reported [Wyart and Â¤6avnic~r1957). Although characteristics that are distinctly different many processes for growing synthetic emerald hydro- from other synthetic emeralds and there- thermally have been described since then (summarized in fore must now be considered when identi- Sinkankas, 1981),until recently only three major produc- fying emeralds. In addition to distinctive tions of hydrothermal synthetic emerald have been com- inclusions such as gold, the Biron synthetic mercially available to the jewelry trade: Linde (patented is inert to ultraviolet radiation, has a spe- process now owned by Regency), Lechleitner (full syn- cific gravity of 2.68 -2.71, and refractive thetic in addition to overgrowth), and, most recently, those indices of = 1,569 and (D = 1.573. This ar- grown in the Soviet Union (see Talzubo, 1979). ticle examines in detail thegemological The synthetic emerald reported on here represents a properties of the Biron hydrothermal synthetic emerald and discusses means of new hydrothcrmal process that can yield unusually clean identifying this new synthetic. faceted stones (figure 1)from remarkably large single crystals (figure2). This material will be commercially available in the latter part of 1985. This new hydrothermal emerald is being synthesized in Western Australia and marketed as faceted stones under the trade name Biron. Note that this is not the same material as the vanadium-doped synthetic ABOUT THE AUTHORS emerald that was grown several years ago in Melbourne, Mr. Kane is research and gem identification Australia, by Taylor (1967). supervisor of the GIA Gem Trade Laboratory, Inc., The manufacturer reports that research on the Biron Los Angeles, California; and Mr. Liddicoat is synthetic emerald began in 1977 in Western Australia. chairman of the board of the Gemological Institute of America, Santa Monica, California. Since then, a few brief notes based on the examination of a very small number of stones have appeared in the Acknowledgments: The authors would like to thank Mr. W.L. Cotton and Biron Minerals Ply., Ltd., tor literature (Brown, 1981 and 1983; Brown and Snow, 1984; the loan and generous donation of some of the syn- Darragh and Willing, 1982; Tombs, 1983).In the interest of thetic material examined in this study; and Bill Kerr providing detailed information to the gemological com- for preparing some samples for analysis and photomicrography. Allphotographs, unless munity on the properties and identifying characteristics of otherwise indicated, are by Robert E. Kane. this synthetic emerald, however, the manufacturer, Biron 0 1985 Gemological Institute of America Minerals Pty., Ltd., and the distributor made available to 156 Biron Emerald GEMS & GEMOLOGY Fall 1985 Figure 1. These faceted Biron hydrothermal synthetic emeralds are representative of many examined in this study. The stones shown here have a hi& clarity and range in weight from 1.20 to 3.00 ct. Photo 0 Tino Hammid, GIA 202 samples of the new Biron synthetic em- to be completely free of inclusions to those that erald. The samples included 150 faceted stones of had areas of visible inclusions. various shapes and cuts (ranging from 0.05 ct to 3.00 ct), 50 preforms (weighing from 1.50 ct to 5.00 PLEOCHROISM ct), and two rough crystals (96.08ct and 108.05 ct). Using a calcite dichroscope, we observed These specimens were examined carefully and dichroism in strongly distinct colors of green-blue subjected to several gemological tests; a few were parallel to the c-axis and yellowish green perpen- also chemically analyzed. A detailed study of the dicular to the c-axis. These results are typically inclusions present was also conducted. The results observed in other synthetic emeralds, as well as in of these examinations and tests are reported below many natural emeralds. and summarized in table 1. SPECTRAL EXAMINATIONS VISUAL APPEARANCE The visible-light absorption spectra of several of The faceted Biron synthetic emeralds studied the faceted Biron synthetic emeralds were exam- varied in hue from green to slightly bluish green in ined with a GIA GEM Instruments spectroscope moderate to vivid saturation (figure 1).The well- unit. The observed spectra appeared to be essen- cut stones were relatively consistent in color with tially the same as the well-known absorption spec- vivid saturation. As would be expected, small tra of emerald described by Liddicoat (1981, p. 194), stones and those that were cut shallow were con- which are the same for both natural and synthetic siderably lighter in tone. emerald, Nearly all of the faceted Biron synthetic When looking down the optic axis direction, emeralds examined were very transparent. When we observed in all of the stones tested a vague examined with the unaided eye and overhead il- general absorption from 400.0 nm to approxi- lumination, they ranged from stones that appeared mately 480.0 nm, a superimposed sharp line at Biron Emerald GEMS & GEMOLOGY Fall 1985 157 by Dr. George Rossman, of the California Institute of Technology, using a Nicolet series 60SX Fourier transform infrared spectrometer system. The spectra, taken from several samples of Biron synthetic emerald, revealed the presence of water, thus confirming that these synthetic emeralds are grown by a hydrothermal process. All natural emeralds and hydrothermal synthetic emeralds contain some water, whereas flux-grown synthetic emeralds contain no water (Nassau, 1980). COLOR-FILTER REACTION Several of the Biron synthetic emeralds were tested with a Chelsea color filter. All of the stones tested revealed a strong red appearance under the filter, as is also the case with many other hydrothermal and flux-grown synthetic emeralds. Un- fortunately, many natural emeralds from various sources show the same reaction. Therefore, the color-filter reaction alone provides no indication of the synthetic origin of this material. SPECIFIC GRAVITY, REACTION TO ULTRAVIOLET RADIATION, AND REFRACTIVE INDICES AND BIREFRINGENCE Figure 2. An exceptional example of the Biron hydrothermal synthetic emerald crystals grown Traditional gemological tests for the distinction of in Western Australia. This crystal measures 3.50 synthetic emerald from natural emerald have cm long by 1.6 cm wide, and weighs 96.08 ct. always considered microscopic examination of Photo by Tino Hammid; @ W. L. Cotton. characteristic inclusions to provide definitive proof of origin. However, this test is often considered the most difficult to master because of the 477.0 nm, a broad band of absorption between similarities of some of the inclusions (such as 580.0 and 615.0 nm, and lines in the red situated at "fingerprints" and "veils") found in both synthetic 637.0, 646.0, 662.0, 680.5, and 683.5 nm. We ob- and natural emeralds. Consequently, many gem- served a similar absorption when we examined the ologists and jewelers have relied on magnification spectrum perpendicular to the optic axis; however, the least, and have arrived at an identification on the sharp line at 477.0 nm was absent. The same the basis of refractive indices, birefringence, reac- absorption features also occur in natural emeralds. tion to ultraviolet radiation, and specific gravity. When the Biron synthetic emeralds were However, with the new Biron synthetic emerald, placed over the opening of the iris diaphragm on as well as with other newer hydrothermal syn- the spectroscope unit, a red transmission was ob- thetic emeralds, such as the Russian material served. This transmission ranged from weak to (Takubo, 1979)) some of these standard tests no very weak, depending on the position of the stone longer provide even a vague indication of synthetic and of the light source, as well as on the size of the origin. stone. We have observed that this phenomenon is typical of many synthetic emeralds and is also Specific Gravity. The specific-gravity values for exhibited by some natural emeralds, inasmuch as the Biron hydrothermal synthetic emeralds were it is occasionally observed in very fine-color determined by the hydrostatic method with a emeralds from Chivor, and in medium to light Voland diamond balance. The sample stones emeralds from Gachalh, in Colombia. showed slight variations in density from 2.68 to Infrared absorption spectra were obtained 2.71. All of the faceted synthetic emeralds were 158 Biron Emerald GEMS & GEMOLOGY Fall 1985 among natural beryls (Flanigen et al., 1967).Just as TABLE 1. The gemological properties of the Biron with natural emeralds, the specific gravity and re- hydrothermal synthetic emerald. fractive indices of hydrothermal synthetic emer- Properties Pleochroisrn Strong: green-blue parallel to alds are also dependent in part on the amount of that overlap the c-axis and yellowish green impurity ions and molecules they contain. Be- with those perpendicular to the c-axis. cause of the different synthesis techniques used, of natural Absorption Optic-axis direction: absorption emeralds spectruma lines at 477.0, 637.0, 646.0, these properties frequently differ from one manu- from (400-700 nrn) 662.0, 680.5 and 683.5 nm; a facturer to another.

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