Research On Gemological And Mineralogicai Characteristics Of Freshwater Nucleated Cultured Pearls Of Jiangxi Province

In this paper，polarized microscopy，Cathode Luminescence（CL），SEM，EMPA， LA-ICP-MS， XRD and IR testing technique are used to study thegemological and mineralogical characteristics of freshwater nucleated andnon-nucleated cultured pearls，and hyriopsis cumingi，which are all from JiangxiProvince. The conclusions are as follows:In X-ray，the nacre in freshwater nucleated cultured pearl shows yellowfluorescence，while the nucleus has no fluorescence. In CL microscope，the nacre infreshwater cultured pearls shows green-yellow fluorescence，aragonite shows red，while nucleus and organic matter presents no fluorescence. Combined with theresults of previous studies seawater pearls are not fluorescent in X-ray and CLinstrument. The main mineral components of the nacre of freshwater nucleated andnon-nucleated cultured pearls and nucleus are aragonite， which infers thisfluorescence differences due to the different element type and content. Using X-rayFluorescence and CL technique，saltwater pearls and freshwater pearls can beidentified， as well as freshwater nucleated and non-nucleated cultured pearls.The picture of SEM expresses that，in the vertical direction of nacre，aragoniteplatelets have the appearance of imbricate structure，however parallel to the directionof nacre，it shows layered structure that similar to the “contour” on the map. Thearagonite platelets in nucleated pearls have the same size，which is different fromno-nucleated pearls. The distance between layers in the former is smaller than thelatter，which attribute to a brighter luster of nucleated pearls.The main chemical component of freshwater nucleated cultured pearls isCaCO3，in addition to trace element such as P，Mn，Sr，Mg，Ba，Fe，K，Cr. Pis of the highest content should be present as the form of organic matter in the pearl.Tested by XRD，the main mineral phase in freshwater non-nucleated culturedpearls and nucleus is aragonite，and also containing a small amount of vaterite.Though calcite has been also detected in the flat pearls from hyriopsis cumingi andnuclear cultured pearls，the content is very low. The lattice parameters measured values of the aragonite is large than the theoretical value，infers that Ca²⁺is replacedby Sr²⁺，Ba²⁺and K+.The IR spectra of freshwater nucleated and non-nucleated cultured pearls，andnucleus suggest that they mainly consist of aragonite. In pearls，[CO₃]^2-，organicmatter and water can cause the infrared vibration bands，as well as other element.1080cm^-1is ν1stretching vibration of [CO₃]^2-，712cm^-1and698cm^-1[CO₃]^2-is ν4bending vibration，1789cm^-1is ν1+ν4vibration，which is stable. While the ν2the ν3vibration of [CO₃]^2-and ν1vibration of H-O-H is slightly different. In addition ν1stretching vibration and ν4bending vibration peak are the characteristic peaks of thearagonite and calcite.