Study On Gemology And Mineralogy Of Quartzite Jade From Dabie Mountain

Quartzite jade deposits in Dabie Mountain area are mainly discoverd at Huoshan,Jinzhai Counties,Anhui Province.This kind of quartzite jade deposits are found within the North Dabie complex zone and North Huaiyang tectonic zone,particularly,North Dabie complex zone in geology.It is kind of low-midium temperature hydrothermal solution related metasomatic deposit.A detailed field geological survey,laboratory research and identification techniques such as the petrographic thin section with polarizing microscope,EPMA,SEM,Chemical analysis,XRF,XRD,FTIR and Raman spectroscopic techniques have been systematic performed in order to analysis and discuss the gemological and mineralogical characteristics of quartzite jade from Dabie Mountain based on the geological survey.It was found that the color of quartzite jade from Dabie Mountain is very rich.It is colorless when the jade is pure.It shows different colors such as yellow,red,green and gray when the jade contains different kinds of impurity minerals.The refractive index is 1.53 or 1.54(spot measurement).The relative density is almost from 2.60 to 2.64.The color is generally stable in the normal ware condition.However,the color fade and de-coloration occur when the material is placed at high temperature environment.The evaluation and grading of the quality of raw and unfinished materials and polished materials should be carred out separately.The grading methods of polished materials could be made based on the luster,transparency,clarity and texture.?-quartz is the major component mineral of the quartzite jade which consists of 70%?100%,depending on different samples.The major impurity minerals are goethite,pyrite,chlorite,potassium feldspar,rutile,brookite,pyrolusite,mica,and clay minerals.These minerals are mostly fine dispersed and distributed along the fissures,and the quartz grain boundaries.The quartz crystals are microaphanitic-microcrystalline-phanerocrystalline aggregates with granular,agglomerate or banded structures.The differences of the microstructures between banded quartzite jade from Dabie Mountain and banded agate chalcedony result from their geochemical conditions of the formations.The crystallinity of SiO2 group minerals has a certain correspondence relationship with the features of FTIR.The quartz and quartzite have sharp bimodal of 800cm-1,780cm-1 and narrow band.The low-frequency bandof chalcedony(agate)is shoulder.Quartz,quartzite and Dabie Mountain samples have weak band of 692cm-1and chalcedony(agate)does not exist or is not obvious.So the crystallinity of quartzite jade from Dabie Mountain is higher than chalcedony(agate)and closer to tradition quartzite.