The Gemological And Mineralogical Characteristics Of Jilin "Panlong Jade"

Jilin "Panlong Jade" is produced in the alteration zone of a large lead-zinc deposit's surrounding rock in Panlong,Jilin Province.It's named Sericite quartzite in petrology.This paper systematically studies the gemological characteristics,mineralogy characteristics and the color causes of the "Ponglong Jade" with modern testing methods.Observation tests showed that "Panlong Jade" is mainly yellow green and dark green,the color distribution is generally uniform.It's mainly formed as blocky,and it shows oily luster to weak glass luster,jagged fracture.The range of the refractive index of this jade is 1.51 to 1.53,the density is ranged 2.64g/cm³ to 2.73g/cm³,the Moh's hardness is 6.75-7.17.The main structure of this jade is cryptocrystalline-fine grained and unequal grain. "Ponglong Jade" is composed of quartz and sericite,sometimes which contains pyrite.The main chemical composition of "Ponglong Jade" are SiO₂ and Al₂O₃ with a small amount of K₂O?FeO,Fe₂O₃?MgO?MnO?TiO and Na₂O.According to the loss of sulfur in pyrite,which indicate it's genesis was related to the hydrothermal alteration.According to the Ti thermometer of muscovite,the metamorphic environment temperature of sericite is about 320°C.The total amount of rare earth elements is stable,which is about 150ppm,showing negative Eu anomalies with?Eu values between 0.18 and 0.22.LREE/HREE ranges from 7.30-9.79,LaN/YbN ranges from 5.67 to 10.48,?Gb_N/Yb_N?approximately equal to 1,?La_N/Sm_N?>1,which shows the enrichment of LREE.The Sm/Nd value indicates that the protolith of"Panlong Jade"is sedimentary rock derived from the shell.Tested by FTIR,the characteristic spectrum is dominated by quartz characteristic peaks and contains weak sericite peaks.The laser Raman spectrum shows in the light position of the sample,the characteristic peak of quartz is dominant and the characteristic peak of sericite is weak.In the color-enriched region,the characteristic peak of sericite is dominant,which may contain characteristic peaks of some quartz minerals.Combined with microscopic magnification observation,it is found that the color of jade is enriched in the sericite matrix between colorless quartz particles,which indicates that the color of"Panlong Jade"is caused by sericite.The ultraviolet-visible spectrum shows an absorption peak at 726nm due to the electric charge transfer from Fe²⁺to Fe³⁺.XRF data shows that the value of w(Fe³⁺)/w(Fe²⁺)is significantly higher in yellow-green samples than that in dark green samples,which indicate the color of sericite in "Panlong Jade" is caused by the absorption of ferric ion.