The Gemology Characteristics Of Green Garnet

A comprehensive study of the gemological properties of green garnets such as demantoid,tsavorite,Mali garnet,Uvarovite by means of modern testing methods such as gemological tests,UV-visible spectroscopy,Infrared spectroscopy,Raman spectroscopy and Electron probe in this paper,and statistical methods were used to establish the link between garnet components and spectra.The garnet species can be initially determined by conventional gemological test and inclusion characteristics.The relative density of demantoid,Mali garnet and tsavorite decreases in turn.Mali garnet has a higher refractive index than tsavorite.The refractive index of Mali garnet is linearly positively correlated with relative density.The EMPA results show that the main component of demantoid is Andradite,the main component of tsavorite is Grossularite,the main component of Mali garnet is Grossularite-Andradite,and the main component of Uvarovite is Uvarovite and Grossularite.The iron-aluminum ratio of Grossularite-Andradite is defined as RAM,the refractive index and relative density of Grossularite-Andradite are positively correlated with the RAM,in the other word,as the iron content increases,the refractive index and relative density of Grossularite-Andradite become larger..Ultraviolet-visible spectroscopy tests indicate that the yellow-green color of demantoid is colored by Fe³⁺and Cr³⁺,the green of tsavorite is colored by Cr³⁺and V³⁺,the yellow-green of Mali garnet is colored by Fe³⁺and Cr³⁺.In the infrared spectrum of the green garnet,the peaks of A,B,C,D,F,G,and H are linearly and negatively correlated with the unit cell parameters of the corresponding sample,the IR absorption peaks of the samples were shifted to the shortwave numbers with the increase of the cation radius.The E peak is related to the content of Pyralspites,and the G peak has a linear negative correlation with the Fe content.The content of Andradite can be roughly judged by the G peak.The Raman displacements of the A_1g and T_2g modes belonging to?Si-O?_Str,the A_1g.