Identification of Nephrite Gravel with Organic Imitated Skin

Recently a kind of nephrite gravel (Ziliao in Chinese) imitation has appeared in the Chinese nephrite market. This nephrite gravel imitation is in fact primary nephrite (Shanliao in Chinese) or slope-wash deposit nephrite (Shanliushuiliao in Chinese), which was rounded off and further dyed and manufactured skin by using polymer materials. The appearance of this nephrite gravel imitation is close to nephrite gravel with weathering crust, so it may be deceptive to consumers. Thus, the conventional gemmological testing methods, EPMA and FTIR were used to compare the conventional gemmological characteristics, chemical composition, and infrared spectra between nephrite gravel and nephrite gravel imitation. The results show that, there are differences between nephrite gravel and nephrite gravel imitation, such as surface topography characteristics, refractive index and density, while the fluorescence of nephrite gravel and nephrite gravel imitation tend to be the same. EPMA analysis indicates that the chemical composition of weathering crust of nephrite gravel contains a higher content of FeO_T than its fresh layer. However, the chemical composition of artificial crust of nephrite gravel imitation can hardly be precisely tested by EPMA analysis. FTIR analysis shows that both fresh layer and weathering crust of nephrite gravel have a characteristic infrared spectral feature of tremolite, so does the fresh layer of nephrite gravel imitation;while artificial skin of nephrite gravel imitation has a characteristic infrared spectral feature of polymer. The absorption bands relating to the vibration and bending modes of C=O and C-H in polymer appear at 1 730, 1 452 cm^-1 respectively. Hence, it has certain significance of applying surface topography characteristics observation, refractive index testing, chemical composition and infrared spectra analysis to separate authentic nephrite gravel and nephrite gravel imitation dyed by organic stuff.