BERILLIUM DIFFUSION IN TREATED CORUNDUM: ANALYSIS AND IDENTIFICATION I. Adamo1,2, G.D. Gatta1, Caucia F.3, V. Ntolia 1, Prosperi L.2 1 Dipartimento di Scienze della Terra, Università degli Studi di Milano, Italy 2 Istituto Gemmologico Italiano; Milano, Italy 3 Dipartimento di Scienze della Terra, Università degli Studi di Pavia; Italy Corresponding author’s email address: firstname.lastname@example.org At the end of 2001, unprecedented amounts of saturated orange and orangy pink (the so-called “padparadscha”) corundums became widely available to the worldwide jewelry market. Many studies subsequently revealed that the light element beryllium (Be) had been diffused into a wide range of corundum gems in order to alter/produce their color. The Be diffusion process requires heating at high temperature (over 1750 - 1800°C) in oxidizing atmosphere, using beryllium-bearing additives (chrysoberyl or beryllium oxide). At the present, a full range of colors, including yellow, blue and red, have been produced or altered by Be treatment, sometimes used in combination with traditional heating. The beryllium diffusion process is surely the most broadly applicable treatment to induce coloration in corundum so far achieved, explaining the extraordinary effect on the market. Consequently, the analysis and identification of Be diffused corundum and its separation from untreated or traditionally heated counterpart has become a major issue in the gem trade. The observation of Be-diffused corundum at optical microscope can result useful for identification. Diagnostic evidence is an anomalous color distribution, characterized by a layer of surface-conformal color induced by Be-diffusion, which however is not visible when the corundum was colored throughout. Other microscopic evidences indicative of an exposure to very high temperatures, as those typically used for Be-diffusion, are features of inclusions significantly altered, melted or internally recrystallized during the treatment (e.g., highly altered zircon inclusions with whitish crusts of baddeleyite). Spectroscopic techniques (e.g. UV-Vis-NIR, IR, Raman) have been employed to provide identification criteria, but they do not allow a separation from the natural or traditionally heated corundum. At the present, the only reliable identification of Be-diffused corundum is based on the detection of trace levels of beryllium, by means of advanced chemical analyses, such as secondary ion mass spectrometry (SIMS), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and laser-induced breakdown spectroscopy (LIBS). The detection of Be amounts >1 wt ppm (generally 4-15 wt ppm, rarely up to 50 wt ppm) allows us to surely identify the stone as Be-diffused and the laboratory report should state that the gem shows “indication of heating and color induced by diffusion of a chemical element from an external source”. Single-crystal X-ray diffraction and polarized Raman spectroscopy were used to provide additional identification aids, but structural parameters (i.e., cell parameters, bond distance, thermal displacement parameters) and Raman spectra do not change significantly between Be-diffused and untreated specimens.
Berillium diffusion in treated corundum: Analysis and identification / I. Adamo, G.D. Gatta, F. Caucia, V. Ntolia, L. Prosperi. ((Intervento presentato al convegno 87. Congresso della Società Geologica Italiana e 90. della Società Italiana di Mineralogia e Petrologia tenutosi a Milano nel 2014.
|Titolo:||Berillium diffusion in treated corundum: Analysis and identification|
GATTA, GIACOMO DIEGO (Secondo)
|Data di pubblicazione:||set-2014|
|Settore Scientifico Disciplinare:||Settore GEO/09 - Georisorse Miner.Appl.Mineral.-Petrogr.per l'amb.e i Beni Cul|
|Enti collegati al convegno:||Società Geologica Italiana|
Società Italiana di Mineralogia e Petrologia
|Citazione:||Berillium diffusion in treated corundum: Analysis and identification / I. Adamo, G.D. Gatta, F. Caucia, V. Ntolia, L. Prosperi. ((Intervento presentato al convegno 87. Congresso della Società Geologica Italiana e 90. della Società Italiana di Mineralogia e Petrologia tenutosi a Milano nel 2014.|
|Appare nelle tipologie:||14 - Intervento a convegno non pubblicato|