Study on Gemmological Characteristics of an Imitated Aquamarine

Recently, Gem Appraisal Center of Peking University in daily inspection has received some samples claimed to be "aquamarine".The shapes of samples are various, such as cabochon and faceted bracelets.Aquamarine is a light blue, green-blue to blue-green beryl, an important gem of the beryl family.The English name of aquamarine comes from Latin, meaning "seawater", which indicates its resemblance to the colour of seawater.Aquamarine wins people's affection with its elegant, beautiful sky blue colour.It has been popular since the middle ages, and has a long history.The gem industry also declares it as the birthstone of March, symbolizing composure, braveness and courage.Due to the price increase of natural aquamarine recently, there is a large variety of imitations in the market, most of which can be easily distinguished from aquamarine.But the samples in this paper have a relative high degree of similarity.First, conventional instruments are adopted to test refractive index, relative density and hardness of the samples.Resultsshow that the samples have refractive index of 1.54, relative density of 2.66and Mohs' hardness of 7.Although these conventional gemmological parameters of the samples are similar to those of aquamarine, the characteristics in magnification observation are different for both.The magnification observation shows that blue colour in the samples is distributed along the fractures, which is nondirectional.The distribution characteristics of colour in the samples are caused by dyeing.It is important to note that the natural fractures in the aquamarine is also common, which is hard to be distinguished from that of dyeing samples by naked eye.Therefore, more careful observation is required.The fractures in natural aquamarine are usually oriented, and colour is well distributed.The samples under polariscope show all-bright phenomenon, an indication of a heterogeneous aggregation.It is clearly different from aquamarine, a member of hexagonal system, which shows "four bright and four dark" phenomenon.In order to determine its authenticity, Fourier transform infrared spectrometer is used to analyze the samples.Reflection method is used for their mineralogical species and the results show that the mineral component is quartz.Combining the previous test results, it is concluded that the samples are dyeing quartzite.Compared with the general dyeing quartzite, the dyeing quality of the samples are obviously much better.Since quartz class exists widely in the crust, it is cheap, easy to obtain, and is often used to imitate all kinds of gemstones.Gemmologists should always pay attention to them.Although the samples in this paper are similar to aquamarine in appearance, as well as conventional gemmological parameters, some of its magnification characteristics are different from those of aquamarine.The authors suggest that inspection institutions should focus on the identification characteristics of aquamarine, by microscope and polariscope.If suspicious feature is noticeable, other testing methods should be used.