Identification Characteristics of Gem Material Called“Cinnabar”from Jewelry Market

In recent jewelry market,a kind of red stone called"cinnabar"appears and is sold as cabochon bracelets or carvings.Cinnabar in history is well known as a sort of Chinese traditional medicinal material to make people feel sedative.On the basis of previous research,the main chemical composition of medical cinnabar is HgS and its content is nearly 86%-89%.To make sure the mineral components of"cinnabar"from jewelry market,two pieces of carvings and a cabochon bracelet are studied by conventional gemmological instruments for its general parameters.Infrared spectrometer(IR),X-ray powder diffraction spectrometer(XRD),laser-induced breakdown spectroscopy(LIBS)and polarizing microscope are used for further research.According to the results of conventional tests, the refractive index of sample is about 1.56 and specific gravity is 2.24-2.25. Under long wave ultraviolet light, the samples present weakly red fluorescence, while they are inert under short wave.The results of XRD show that the main mineral components in samples are dolomite and barite, with chemical formulas are CaMg(CO₃)₂ and BaSO₄, which are quite different from Chinese traditional medicinal material cinnabar.According to infrared spectrum, the absorption peaks of samples in the fingerprint region prove the existence of dolomite and barite, but it is a little different from dolomite and barite. The absorption peaks in the region of 2 800 to 3 000 cm^-1 attribute to methyl (-CH3) andvinyl (-CH=CH₂), which indicates the existence of organic matters in the "cinnabar" samples.The result of LIBS shows the peaks of Ba, Ca, Mg apparently. Moreover, the obvious peak of C element confirms the existence of organic matters, because the C element almost can not be found in any natural inorganic substances.Polarizing microscope was used to observe the mineral structure of samples. lt can be clearly seen that under orthogonal polarizing microscope, granular dolomites scatter uniformly all over the vision, as well as the barite. Each kind of mineral particle has nearly the same size,which indicates that the samples were artificially pressed rather than natural produced.Under single polarizing microscope, the red material spreads over intricately without any mineral form. Further more, the mineral is stained along to border by those red material,which suggests the red colour of the sample is caused by the red dye.In a conclusion,the sample from jewelry market is pressed artificially by some mineral,such as dolomite and barite, and is dyed by a kind of red organic dye, which is quite different from the Chinese traditional medicinal material.