Confocal Micro-Raman Spectroscopy: A Powerful Tool to Identify Natural And Synthetic Emeralds

o separate natural from synthetic emeralds, or determine the geographic origin of a natural stone or the growth technique of a synthetic, a gemologist can use microscopy, chemical analysis, and FTIR spectroscopy.Although there are varying degrees of overlap in features seen or analyzed, in many cases each method can lead to a good identification.Here we introduce another tool for determining emerald origin-confocal Raman spectroscopy.This method provides some distinct advantages over previous techniques.For example, traditional FTIR analysis requires that 2 mg of material be pulverized and mixed with KBr powder (Schmetzer and Kiefert, 1990), and then the powder needs to be pressed into a thin disk, making this a destructive and time-consuming technique.Microscopic determination requires a trained and experienced gemologist, and is only effective if the sample contains diagnostic inclusions.Chemical analysis can sometimes determine geographic origin as well as synthesis technique based on the concentrations of some minor or trace elements (e.g., Hänni, 1982;Schrader, 1983;Stockton, 1984;Yu et al., 2000).However, there is chemical overlap among some origins.This article describes the use of confocal micro-Raman spectroscopy to classify water types in the structural channels of emeralds, to differentiate natural vs. synthetic emeralds (including the form of synthesis), and to investigate geographic origin (figure 1).Raman spectrometers with confocal capability are available in many gemological laboratories, and the analysis is rapid and nondestructive.