Characterization of the New Malossi Hydrothermal Synthetic Emerald

CHARACTERIZATION OF THE NEW MALOSSI HYDROTHERMAL SYNTHETIC EMERALD Ilaria Adamo, Alessandro Pavese, Loredana Prosperi, Valeria Diella, Marco Merlini, Mauro Gemmi, and David Ajò A new production of hydrothermal synthetic emeralds, grown in the Czech Republic with Italian technology, has been marketed since December 2004 with the trade name Malossi synthetic emerald. Several samples were investigated by standard gemological methods, combined with chemical analyses and UV-Vis-NIR and IR spectroscopy. A comparison of this material with natural and other synthetic emeralds (the latter grown by the flux and hydrothermal techniques) reveals that Malossi hydrothermal synthetic emerald can be identified on the basis of microscopic features and chemical composition, along with the mid-infrared spectrum. ecause of emerald’s commercial value, a tures of Malossi synthetic emeralds that can be used remarkable number of synthetic emeralds, to distinguish this material from natural and other Bgrown by flux and hydrothermal processes, synthetic (hydrothermal and flux) emeralds. have entered the market over the past five decades. The hydrothermal synthetic emeralds are particu- larly notable in terms of the quantity produced and GROWTH TECHNIQUE their availability (see, e.g., Kane and Liddicoat, Malossi synthetic emeralds are grown at about 1985; Koivula et al., 1996; Schmetzer et al., 1997; 450°C in a small rotating autoclave that is lined Koivula et al., 2000; Chen et al., 2001; Mashkovtsev with gold and carefully sealed. A seed of natural yel- and Smirnov, 2004). low beryl, suspended by a platinum wire, is used to The present study focuses on a new hydrother- help initiate growth. Concentrated hydrochloric mally grown synthetic emerald manufactured since acid is usually used to prevent Cr (the only chro- 2003 in Prague, Czech Republic. This new gem mophore used) from precipitating. Large crystals of material, called Malossi synthetic emerald (figure 1), the synthetic emerald can be grown in 40–60 days has been marketed since December 2004 in Italy by (A. Malossi, pers. comm., 2005). Arsaurea Gems (Milan) and in the U.S. by Malossi Inc., the U.S. subsidiary of Malossi Created Gems (Raleigh, North Carolina). Currently, about MATERIALS AND METHODS 5,000–6,000 carats of the faceted synthetic emeralds For this study, we examined 30 emerald-cut gems are produced per year, and this rate is expected to and 5 rough samples of the new synthetic emerald, increase (A. Malossi, pers. comm., 2005). The crystals produced so far range from 25 to 150 ct, with a mean weight of about 77 ct, and the largest faceted See end of article for About the Authors and Acknowledgments. stone obtained weighs about 15 ct (A. Malossi, pers. GEMS & GEMOLOGY, Vol. 41, No. 4, pp. 328–338. comm., 2005). In this article, we report those fea- © 2005 Gemological Institute of America 328 MALOSSI HYDROTHERMAL SYNTHETIC EMERALD GEMS & GEMOLOGY WINTER 2005 Figure 1. Malossi synthetic emeralds are grown by a hydrothermal technique in the Czech Republic, using Italian technology. These crystals (28.40– 141.65 ct and 7.1–69.9 mm) and emerald cuts (1.34–7.89 ct) are some of the samples examined for this study. Photo by Alberto Malossi. which were provided by A. Malossi (see, e.g., figure Room-temperature nonpolarized spectroscopy in 1). The faceted samples weighed 1.34–7.89 ct, and the visible (460–750 nm), near-infrared (13000–4000 the rough specimens ranged from 28.40 to 141.65 cm−1), and mid-infrared (4000–400 cm−1) regions ct (30.0–69.9 × 10.8–22.5 × 7.1–14.8 mm). Repre- was carried out on all Malossi, Russian, Biron, and sentative faceted samples of hydrothermal syn- Linde-Regency samples. We used a Nicolet NEXUS thetic emeralds from other commercial sources (all FTIR-Vis spectrometer, equipped with a diffuse from the collection of the Italian Gemological reflectance accessory (DRIFT), which had a resolu- Institute) were studied for comparison: Russian (5), tion of 4 and 8 cm−1 in the infrared and visible Biron (5), and Linde-Regency (1). In addition, litera- ranges, respectively. ture comparisons were made to other synthetic Mid-infrared spectroscopy (4000–400 cm−1) was emeralds produced by the hydrothermal technique also carried out in transmission mode using KBr (Chinese, Lechleitner), as well as to flux synthetics compressed pellets with a 1:100 ratio of sample:KBr. and natural emeralds. Since this is a destructive technique, we restricted All the faceted samples were examined by stan- these IR measurements to portions of two rough dard gemological methods to determine their opti- specimens only. cal properties (refractive indices, birefringence, and Additional UV-Vis-NIR reflectance spectra were pleochroism), specific gravity, UV fluorescence, and recorded by an Avantes BV (Eerbeek, the Nether- microscopic features. lands) apparatus equipped with halogen and deuteri- Preliminary qualitative and semiquantitative um lamps and a CCD spectrometer with four grat- chemical analyses of 11 faceted synthetic speci- ings (200–400 nm, 400–700 nm, 700–900 nm, and mens (8 Malossi, 1 Russian, 1 Biron, and 1 Linde- 900–1100 nm), a 10 µm slit, and a spectral resolu- Regency) were obtained by a Cambridge Stereo- tion of 0.5 nm. A polytetrafluoroethylene disk scan 360 scanning electron microscope, equipped (reflectance about 98% in the 400–1500 nm range) with an Oxford Isis 300 energy-dispersive X-ray was used as a reference sample. spectrometer, for the following elements: Si, Al, V, X-ray powder diffraction was also used to inves- Cr, Fe, Ni, Cu, Na, Mg, and Cl. Quantitative tigate an incrustation on the surface of one chemical data (for the same elements) were Malossi synthetic emerald crystal. Measurements obtained from these same 11 samples using an were performed at room temperature, by means of Applied Research Laboratories electron micro- a Bragg-Brentano parafocusing X-ray powder probe fitted with five wavelength-dispersive spec- diffractometer Philips X’Pert, in the θ−θ mode, trometers and a Tracor Northern energy-dispersive with CuKα radiation (λ = 1.5418 Å), over the range spectrometer. of 5° to 75° 2θ. MALOSSI HYDROTHERMAL SYNTHETIC EMERALD GEMS & GEMOLOGY WINTER 2005 329 RESULTS AND DISCUSSION Gemological Testing. The standard gemological properties obtained on the 30 faceted Malossi samples are summarized in table 1. All the samples were transparent, with a bluish green color. They exhibited strong dichroism in yellowish green and bluish green. Their R.I. and S.G. values: (1) overlapped those of their natural counterparts, especially low-alkali emeralds from various geographic localities (such as Colombia and Brazil; Schrader, 1983); (2) were simi- Figure 2. Straight, parallel growth bands, which also lar to those we measured in Biron and Linde- may be present in natural emeralds, are seen in this faceted Malossi synthetic emerald. Photomicrograph Regency synthetics, and to those reported for Lech- by Renata Marcon; magnified 30×. leitner and Chinese synthetic emeralds (Flanigen et al., 1967; Kane and Liddicoat, 1985; Schmetzer, 1990; Webster, 1994; Schmetzer et al., 1997; Sechos, UV radiation. The fluorescence of Malossi synthetic 1997; Chen at al., 2001); but (3) were lower than emeralds might hint at a synthetic origin, although those of our Russian synthetic samples (in agree- a few high-Cr and low-Fe Colombian emeralds also ment with Schmetzer, 1988; Webster, 1994; Koivula have red UV fluorescence (Graziani et al., 1987). et al., 1996; Sechos, 1997). Most flux-grown synthet- The Malossi synthetic emeralds showed a variety ic emeralds from various manufacturers have R.I., of internal features when viewed with a gemological birefringence, and S.G. values that are lower than microscope. Growth patterns of various forms those observed in the Malossi samples (for compari- (straight, parallel, uniform, angular, and intersecting), son, see Flanigen et al., 1967; Schrader, 1983; often associated with color zoning, were widespread Kennedy, 1986; Graziani et al., 1987). The pleochro- in some of the crystals and cut stones (e.g., figure 2). ism and Chelsea filter reaction of the Malossi sam- Irregular growth structures (figure 3), similar to those ples were not diagnostic of synthetic origin. observed in other hydrothermal synthetic emeralds, The various synthetics showed significant differ- were seen in almost all the samples, providing evi- ences in their fluorescence to UV radiation: Malossi dence of hydrothermal synthesis. Six of the faceted synthetic emeralds belonged to a group exhibiting Malossi synthetic emeralds contained seed plates (fig- red UV fluorescence that includes Linde-Regency and Chinese products, whereas Russian and Biron synthetic emeralds are inert to long- and short-wave Figure 3. Irregular growth structures are also seen in Malossi synthetic emeralds. Such features provide evidence of a hydrothermal synthetic origin. Note also TABLE 1. Gemological properties of Malossi hydro- the natural-appearing “fingerprints” in this sample. thermal synthetic emeralds. Photomicrograph by Renata Marcon; magnified 35×. Color Bluish green Diaphaneity Transparent Optic character Uniaxial negative Refractive indices no = 1.573–1.578 ne = 1.568–1.570 Birefringence 0.005–0.008 Specific gravity 2.67–2.69 Pleochroism Strong dichroism: o-ray = yellowish green e-ray = bluish green Chelsea filter reaction Strong red UV fluorescence Short-wave: moderate red Long-wave: weak red Internal features Crystals (probably synthetic phenakite), “fingerprints,” two-phase inclusions, growth tubes, fractures, various forms of growth structures, color zoning, seed plates, irregular growth zoning 330 MALOSSI HYDROTHERMAL SYNTHETIC EMERALD GEMS & GEMOLOGY WINTER 2005 and colorless crystals—alone or in aggregates—were observed in four Malossi samples (figure 6). On the basis of their morphology, birefringence, and refractive index (higher than that of emerald), such crys- talline inclusions are probably phenakite (Be2SiO4), which is somewhat common in hydrothermal synthetic emeralds (Flanigen et al., 1967) and also may provide evidence that the host emerald is synthetic (Kane and Liddicoat, 1985).

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