The Study On Gemological Characteristics Of Fujian Yunxiao Spessartine

The spessartine garnet from Yunxiao county,Fujian province has bright orange color,high transparency,complete crystal shape,and often symbiosis with quartz crystal and feldspar.It can be used as high-quality gemstone and ornamental stone,and has a good market prospect.However,there are few studies on the spessartine in this origin.Therefore,in order to improve the basic gemmological and spectralinformation of the spessartine in this origin,and to contribute to its betterdevelopment in the jewelry market,this paper studies the gemmological and mineralogical characteristics of the spessartine garnet from Yunxiao countyby conventional gemmological testing methods,SEM,XRD,XRF,EPMA,Raman spectrum,Infrared spectrum,UV-Visible spectrum and other modern testingtechniques.Spessartine garnet from Yunxiao county symbiosis with quartz crystal and albite with the complete crystal shape of tetragonal trisoctahedron n{112}and rhombic dodecahedron d{110}.The size is usually between 1 to 10mm with high degree of idiomorphism.The fringe of crystal planes surrounded by plane d{110}often appear on the plane n{112}.Its relative density is 4.1610,and refractive index is>1.78.Fractures,healing fractures and crystal inclusions are common in them.White albite crystals can be seen in them,and octagonal band structure of different shades of orange color can be observed.The characteristics of small crystal surface cracks,thawing pits and growth steps were observed by using Scanning electron microscopy?SEM?.Due to the fact that it contains certain components of almandine,the cell parameter a₀ was slightly lower than the standard value by X-ray powder diffraction test,ranging from 1.1603 nm to 1.1594 nm.According to electron probe analysis?EPMA?,the end-component of spessartine garnet in the samples was the dominant component?Mole percent 95.61%⁹8.70%?,followed by the almandine garnet?Mole percent 0.04%².84%?.It also contains5.80%⁸.61%?Mole percent?F replace O,which indicates that it is the product of late crystallization of magmatic metallogenic material rich in Mn and Al under low pressure with F in the formation environment.The band structure is related to the chemical composition,from the edge to the center,it is a reverse band structure--the content of Al and Mn decreased,while the content of Fe,Mg and Ca increased,which indicates that the late differentiation and evolution of Mn rich magma that formed the spessartine garnet from Yunxiao county was relatively complete,and the environment and component changes were turbulent during the cooling and crystallization process of silicate magma.The distance of peak B(887±3cm^-1)and peak C(867±2cm^-1)of the infrared spectra of spessartine garnet from Yunxiao county is 15²2cm^-1,which is shorter than that in almandine and pyrope due to the A position of spessartine is occupied by Mn with a larger radius.Due to the homogeneity substitution of certain amount of almandine,the Raman displacements attributed to Si-O_Strtr and Si-O_Bendend in the Raman spectrum are generally shifted to the direction of long wave compared with the standard values..The main absorption of UV-visible spectrum are located at 324±2nm?380±2nm?435±2nm,which are related to Mn.The quality evaluation of spessartine garnet from Yunxiao county can be started from these four aspects:color,clarity,weight and cutting.And this kind of spessartine has a broad prospect in jewelry business,ornamental stone market and industrial uses.