Gemmological Characteristic Comparison of Aquamarines from Four Different Origins

Eleven aquamarine samples from four different origins including Pakistan, Tanzania, Vietnam and Namibia were tested in this paper. Conventional gemmological tests, electron microprobe, ICP-MS, infrared spectroscopy and Raman spectroscopy were studied to analyze differences of basic characteristics, chemical constituents as well as spectral features of aquamarines from four different origins. Conventional gemmological tests revealed samples from Pakistan are of comparatively higher refractive indexes and specific gravities, and the colour of Vietnam aquamarine samples is deeper than others. High content of alkalis-Na was measured in Pakistan aquamarine and the Fe content in Vietnam aquamarine is the highest among all the samples. The results of ICP-MS showed obvious amount of Li, Mn, Zn, Rb and Cs, which were different among samples from different origins, including higher content of Mn, Zn in Pakistan aquamarine and the highest content of Cs in Namibia samples. The infrared spectra displayed consistent peaks among 1 200-400 cm^-1 of all the samples except spectra shifting of Pakistani aquamarine. Different absorption peaks of water were also found in different directions through near-infrared spectra. Raman spectra indicated coexistence of both type I water (3 608 cm^-1) and type Ⅱ water (3 598 cm^-1) in Pakistani aquamarine.