Study On Gem Mineralogy And Geochemical Characteristics Of Taishan Jade

On the basis of field investigation and experimental analysis, this paper studiesthe geological characteristic of mining area as well as the mineralogical, geochemicaland gemmological characteristic of Taishan Jade. The paper also deals with thedevolopment of Taishan Jade. By using some conventional gemmological methods,the physical and chemical characteristic of Taishan Jade have been studied in thispaper. According to all of these characteristic, the paper can set up the evaluationsystem of classification for quality of Taishan Jade.The stratum of mining area consists of Quaternary strata and Taishan Group(Shancaoyu Formation) of the Archaean units, the parent rock of Taishan Jade isiherzolite. Because of strong self-alteration, the main mineral component of TaishanJade is serpentine having aphanitic texture. The orebody appears in veiny, lentoid andirregular shapes.The characteristic of orebody, such as identical extention, expansionand contraction, the phenomenon of branch, is obvious.By the help of Polarizing microscope, we can see that the main mineralcomponent of Taishan Jade is serpentine. The serpentine has finest particles inaphanitic texture. According to mineral crystalline morphology, the serpentine can bedivided into two groups: leafblastic texture and lepidoblastic texture. According torelatively granule size, the serpentine can be divided into three groups: equigranularcrystalloblastic texture, inequigranular crystalloblastic texture and mortar texture. TheTaishan Jade has massive structure and piebald structure.By using of chemical analysis, the result shows that iron ions play a leading rolein the cause of color of Taishan Green Jade and Taishan Variegation Jade, theincreasement of iron ions resulting in darkening color. The color of Taishan DarkGreen Jade is caused by magnetite particle. The results of XRD, IR and chemicalanalysis show the main mineral component is antigorite. The characteristic of traceelements of Taishan Jade is close to that of ultrabasic rock. The Taishan Jade is ofhigher content of Cr and Ni, which can be different from that of Xiu Yu fromLiaoning province. The average ratio of Taishan Jade samples' light-REE to heavy-REE is3.730, the differential degree is moderate. Most of samples havenegative Eu anomaly, only a few samples have positive Eu anomaly. The fractionationof inner part of light-REE is moderate, while the fractionation of inner part ofheavy-REE is small.The testing of δD and δ¹⁸O shows the serpentinization of Taishan Jadehappened in continent after the emplacement instead of in ocean. The relationship ofH and O isotope compositions of ore-forming solution of Taishan Jade illustrates thesource of ore-forming solution should be wet precipitation. We can also conjecturethat Taishan Jade should be the product of self-alteration because of what has beenmentioned above.According to the color and pattern, Taishan Jade can be divided into three groups:Taishan Green Jade, Taishan Dark Green Jade and Taishan Pattern Jade.The paperevaluates the quelity of Taishan Jade from five aspects:color, transparency, texture,clarity and lumpiness and sets up an evaluation system of classification for quality ofTaishan Jade according to different colors.