The Gem-Mineralogy And Fluid Inclusion Study Of Tourmaline In Koktokay,Xin Jiang Province,China

Gem-quality tourmaline,because of its rich and varied colors become very popular varieties of gemstones.Xinjiang Altai area is one of the main origins of gem-quality tourmaline in China.This paper through the conventional gemmological testing,EPMA,XRD,FTIR,inclusion test methods to study on chemical composition,crystal structure,IR,fluid inclusion composition and temperature of Koktokay's tourmaline.The tourmaline from Koktokay area is mainly produced in the pegmatite which surrounding rock is quartz mica schist.The color of the tourmalines are pink,rose red,green,bluish green,and black,glass luste,transparent–opaque.The healing cracks perpendicular to c axis,good crystal shape degree,often showing in elongated grain,longitudinal development of crystal surface;and tourmaline,which is associated with quartz,albite,lithium mica,muscovite,beryl;color-zoned tourmalines are associated with lithium mica and albite,good crystallization and differentiation.RI=1.628¹.646,DR=0.018.The average relative density was 3.016,lower than the standard relative density;the dichroism is strong,and determined by the specific color intensity.By the EPMA and XRD,all the samples are belongs to Elbaite to Schorl isomorphism series,which the black tourmalines are Schorl,pink,green,and blue tourmalines are Elbaite.Green to blue green samples with the content of FeO from less to more,the color intensity from shallow to deep;pink samples with MnO content from less to more,pink tones also showed a change from shallow to deep description of the main coloring element content directly affect the corresponding tone.In this area,there are few vacancies on the X position,because of the influence of the content of Fe,Mg,Li,the unit cell parameters of tourmaline in this area are slightly different from the standard values.The FTIR spectra in the hydroxyl or water molecular vibration section,there are water or hydroxyl in tourmaline crystal,in the range of 3800cm^-1-3000cm^-1,the T2-w?schorl?sample showed a single peak absorption and other samples?elbaite?showed double absorption peak,which is due to vibration caused by different forms of hydroxyl,reflects the crystal structure of these two types of tourmaline the different.There are a lot of gas-liquid inclusions in the samples,mainly liquid inclusions,which belong to the NaCl-CaCl-H₂O system,the crystallization temperature range of tourmaline is 117³35?,estimate the salinity of 1.90%³.77%,estimating the pressure of 12.5560MPa¹8.4614MPa,the ore-forming fluid is rich in Na⁺,Ca^2+,which indicated that tourmalines from Koktokay,Xinjiang are formed in late hydrothermal.