Gemological-Mineralogical Characteristics Analysis Of Serpentine Jade In Ji'an,Jilin Province

Based on the conventional gemological testing,polarized light microscopy,ultraviolet-visible spectroscopy,electron probe,X-ray powder diffraction,infrared spectroscopy,Raman spectrum method and other methods,to research and analyze the mineral composition,chemical composition,color origin,and spectroscopy characteristics of serpentine jade produced in Jilin Ji'an.The color of serpentine jade produced in Ji'an is mainly yellow-green series,including light yellow-green,yellow-green,dark yellow-green and black yellow-green,etc.;it has a cryptocrystalline structure and a block structure;it is mainly waxy luster and grease luster;most jade is opaque,a few are slightly transparent.The refractive index is 1.54?1.55,the relative density is 2.51?2.60,and the range of Mohs hardness varies greatly,ranging from 4.43 to 5.59,which may be due to the change of the test position,the higher hardness of olivine and the lower hardness of serpentine.It is inert under long-wave and short-wave ultraviolet fluorescent lamps.It shows that the Fe²⁺-Fe³⁺charge transfer and the d-d electronic transition of Fe³⁺ions are the main causes of the color of serpentine jade by ultraviolet-visible spectroscopy.Some serpentine jade produced in Jilin Ji'an has a single composition,mainly have serpentine,but also scattered magnetite,calcite and other minerals;and some serpentine jade's main mineral is serpentine,and the minor Minerals include forsterite and brucite,as well as scattered phlogopite and other minerals.This difference in mineral composition is due to the different degree of serpentinization in serpentine jade.Serpentine minerals mainly present leaf-like metamorphic structure,scale-like metamorphic structure and microscopic cryptocrystalline structure.Serpentine minerals in serpentine jade mainly grow in lamellar growth layers alternately,a small amount of which is irregular granular,short columnar and long columnar growth,and the whole has a microscopic cryptocrystalline structure.Part of the serpentine jade retains the granular illusion of olivine.The intersection of the three granular olivines is about 120°,and the boundary line is straight to form a three-sided inlaid granular metamorphic structure,showing a metamorphic structure;there are also some snakes There are remnants of forstrite inside the jade,showing the residual structure of metasomatism.According to the analysis of infrared spectrum and Raman spectrum,the serpentine in Ji'an serpentine jade is mainly composed of lizardite.At the same time,a small amount of chrysotile was found in some samples.The chrysotile was distributed in the chrysotile in the form of veins and fine grains,which may have been formed later.The chemical composition of serpentine mineral is basically the same as the theoretical chemical composition.The content of Mg O in the remaining forsterite in serpentine jade is56.20%?57.46%,which is consistent with the ideal chemical composition of forsterite,and is close to pure forsterite,and its Fe iron content is extremely low.Jilin Ji'an serpentine jade is formed from forsterite through hydrothermal alteration and serpentinization.Combined with the analysis of electron probe experiments,it is inferred that the original rock of the serpentine jade in this article is entirely composed of forsterite,It is an ultrabasic pure peridotite.