Gemological-mineralogical Characteristics And Genetic Analysis Of "Ganlan" Jade In Ji'an,Jilin Province

"Ganlan jade",produced in Caiyuan Town,Ji'an City of Jilin Province,is mainly composed of olivine and serpentine.There will be black veins formed by the combination of other minerals among the"Ganlan jade",most of which are distributed around with the black veins.On the basis of analytical methods such as polarizing microscope observation,electron probe test analysis,XRD analysis,Infrared spectroscopy analysis and Raman spectroscopy,this paper aims to study the gemological mineralogical characteristics of black"Ganlan jade".Besides,this paper makes an analysis of the cause of black"Ganlan jade"and its black veins based on predecessors'research results.External observation and microscopic structure observation have revealed that the essential minerals of the jade part of the black"Ganlan jade"are olivine and serpentine,and the primary minerals of the black veins are Phlogopite,Dravite,Pyroxene,etc.Other minerals include Magnesite,Calcite,Talc,Hornblende and Pyrite.Phlogopite has high purity,Pyrite is embedded in the crevices of the Phlogopite,Dravite's mesh-structure shows that it was reformed by hydrothermal filtration in the late stage of formation,the residual structure of Pyroxene shows that it's the early mineral of metamorphism.It is concluded,by using an EMPA test to analyze the main minerals in"Ganlan jade"and its black veins,that the main minerals in the jade are Forsterite and Lizardite,the Pyroxene in the black veins is Enstatite,and the other minerals in veins include Aliettite,Tremolite,Magnesiocummingtonite and other minerals.Based on data comparison,it is found that the Fe²⁺content is an important factor affecting the color of"Ganlan jade".Additionally,it is speculated that the minerals formed in the later period are characterized by high iron content.XRD experiment analysis shows that the phlogopite in this area features 1M type octahedral structure,and is high in its purity,all of which provide an important clue to the study of genetic types.The results of further judgement on the mineral species are consistent with that of the electronic probe by comparing Standard Infrared spectroscopy with Raman spectroscopy,and by putting the peaks of the test results in place.The Raman spectrum of Forsterite indicates that it is Mg-rich Forsterite,it shows that the area is rich in Mg and poor in Fe;the Raman spectrum of serpentine proves this mineral is Lizardite;the Raman shift of Phlogopite indicates that the later-form Phlogopite has higher Fe²⁺;Dravite's Raman spectrum has a broad vibration peak shows that its crystallinity is poor.Combined with the analysis of the predecessors,the experimental results show that black"Ganlan jade"and black veins are the cause of regional deterioration.In the early stage of metamorphism,Forsterite serpentinization and Carbonateization formed Lizardite,Talc,and Magnesit;Talc dehydrated at about 650?to form refractory Enstatite;in the medium-term of the metamorphism,Forsterite and Lizardite decompose and release MgO into the metamorphic solution;in the later period of the regional metamorphism,a large amount of the B-containing solution entered the magnesite layer,the free MgO combined with B caused the Dravite to be enriched into ore,the Forsterite was further metabolized into serpentine and Phlogopite,and enabled the precipitation and crystallization of Pyrite.The FeO released from the original rock and the Fe²⁺in the hydrothermal fluid re-infiltrate into the"Ganlan jade"to increase the Fe²⁺content and turn the color into black.