The Study On Gemology And Mineralogy Of Zhanguo Red Agate From Xuanhua District,Hebei Province

Zhanguo Red Agates from Xuanhua District,Hebei Province,were mainly produced in Beipo village,Dishuiya village and other places in Xuanhua District.Because of its rich colors,tough texture and beautiful lines,people love it very much.Combining with the results of previous studies,the gemology characteristic,mineral components,color mechanism and cause of structure of Zhanguo Red Agates from Xuanhua District,Hebei Province have been studied in this thesis,with the experiments including routine gemological tests,observation under microscope,infrared spectra,XRD,Laser Raman Spectrum Analysis,UV-Vis-Infrared Spectrum etc.The appraisal standard of Zhanguo Red Agate and issues are also discussed,based on the market.Zhanguo Red Agate is a kind of cryptocrystalline quartz mineral.It has glossy luster and many colors incluing yellow,red,pink,white and black with the relative density from 2.62 to 2.65 and hardness from 6 to 7.The texture of Zhanguo Red Agate under the Polarizing microscope can be divided into tiny grains,short fiber,long fiber and phanerocrystalline quartz.The Boundary between Growth Regions are found out in the fibrous texture and perpendicular to the intersection of two curved bands or sprue center.The orientation of the crystals are symmetrical on each side of the Boundary between Growth Regions.The main mineral of Zhanguo Red Agate is quartz as well as the main mineral of the green surrounding rock is celadonite.LA-ICP-MS is quoted in Zhanguo Red Agate for the first time.The results indicate that the elements of Mn and Fe lead to the dark.Besides the element of Fe,Co is also contributes to the yellow of Zhanguo Red Agate.The data by Micro-Raman Spectrum indicates that moganite is in textures except the phanerocrystalline quartz.Goethite can probably lead to yellow,pink,dark.And pure hematite can produce dark red while orange-red is caused mainly by both goethite and hematite.In addition,the inclusion of radial pattern in crystal cluster is goethite.Combining previous research of agates formation,this thesis speculates the formation mechanism of Zhanguo Red Agate: rich silicon hydrothermal crystallization are attached to the hole wall.Then goethite,hematite and other hydroxides of iron precipitate out from hydrothermal solution,forming different color band.Eventually when the fiber structure stop growing,crystalline quartz fill the rest space.New hydrothermal may carry iron minerals from surrounding rock by the late crack into the inside,which makes the warring states period superposition of onyx appeared color or a color along the fissures.