Studies On The Composition And Structural Characteristics Of Three Gem-Quality Red Coral Species

Gem-quality red coral is one of the most important organic gems.The samples in this paper are Corallium japonicum?Aka coral?,Corallium elatius?Momo coral?from Taiwan-Japan sea area,and Corallium rubrum?Sadinia coral?from Mediterranean sea area.In order to compare the similarities and differences in spectral characteristics,chemical composition and structural characteristics of three Gem-Quality red coral species,the samples were tested by Polarizing Microscope,SEM,Electron Microprobe,ICP-MS,XRD,UV-vis,FTIR and Raman Spectrometer.In addition,the origin characteristics of coral are summarized.Based on the composition and structural characteristics of corals,the biomineralization mechanism of coral skeleton was discussed.The three coral species showed significant origin characteristics in trace element content.Compared with Corallium japonicum and Corallium elatius,the maximum values of F,Ce,Ti,Zn,Al and Ba in Corallium rubrum were the lowest,while the Fe were the highest.In the distribution pattern of rare earth elements,Japanese red corals and red corals show right inclined type,with obvious enrichment of light rare earth elements,while slender red corals are flat type and LREE are slightly enriched.The REE characteristic combinations of the three coral species are different,which has the significance of identification of species and origin.The main mineral composition of corals is high Mg calcite.The molar ratio of Mg/Ca and Sr/Ca in sclerites is higher than that in medullar zone of coral.It represents the different mineralization mechanism between sclerites and medullar zone of coral.The UV-vis spectra of the three species of corals show wide absorption bands at400-550 nm and weak absorption bands at 277,282 and 312 nm.The location and intensity of absorption bands are related to the color of corals.It is speculated that these absorption bands may be caused by aromatic amino acids.Infrared transmission spectra showed calcite peaks at 717,876,1083 and 1435 cm^-1.The peaks at 3445,2925,2851 and 1800 cm^-1 were absorption peaks of the N-H bonds of amino compounds,methylene of aliphatic compounds,carboxyl,C=C bonds of aliphatic compounds and other organic functional groups.In Raman spectra,the intensity of characteristic peaks such as 1128 cm^-1 and 1516 cm^-1 will increase with the deepening of coral color.The Raman peaks of calcite in white cores of Corallium japonicum,Corallium elatius and Calcite minerals shift to the low frequency region in turn,which can be used as the characteristics of coral species identification.The structures of submicrometer crystalline units,microprotuberances,vortices and radioactive bands are quite different among the three coral species,which are reflected in their size,shape and arrangement.Among them,the unit size of Corallium japonicum is the smallest and most orderly,and the boundary of its crystal unit is the most straight.Corallium rubrum was the second,Corallium elatius was the worst.The extinction phenomenon of samples under orthogonal polarization also confirms that the order of calcite crystal units in coral skeleton are as follows:Corallium japonicum>Corallium rubrum>Corallium elatius.The skeleton of Coral are multi-level nested structures,each of which is composed of smaller structural units.Under the control of organic matter,calcite crystals are assembled step by step from Nanodomains to Submicrometer crystalline units,Rhombic plate units,Fiber bundles,Herringbone structural units,Radioactive bands to macro-scale coral skeletons.The mineralization growth of coral skeleton is realized by molecular recognition of organic-inorganic interface and the growth of crystal vortex dislocation.