Identification Characteristics of Weathering Crust for Nephrite Gravel and its Imitation

The price of nephrite gravel (alluvial deposits nephrite) is becoming higher and higher duo to the growing market demand, and more and more imitations are produced.In this paper, nephrite gravel, primary nephrite with natural secondary weathering crust and artificial weathering crust imitation were tested by means of magnifier, gemological microscope, ultraviolet-visible absorption spectroscopy(UVS), and scanning electron microscopy and energy spectrometer (SEM-EDXRF) so as to explore the difference between natural and artificial weathering crust.The results show that nephrite gravel presents the surface features as "sweat pores" and "nail pattern" etc, and dendrite growth pattern for secondary weathering crust color, while the colors of dyed imitation are bright, and concentrate in the epidermis and fissures; the absorption peaks of natural black, yellow, and brown secondary weathering crust color are related to Fe +3 and Fe +2 for lightwave selective absorption, while artificially weathering crust imitation presents the large absorption band extending from the ultraviolet to the visible region, and Fe and Mn are not detected by SEM-EDXRF, which can be used as evidence for identification of the nephrite gravel and its imitation.