Petrology And Gemological Characteristics Of Peridot In Jilin Jiaohe

Jiaohe olivine of Jilin province is one of two major mining area in China.The author takes the olivine of Jiaohe in Jilin province as the research object.The research is based on laboratory analysis via hand specimen observation,polarizing microscope observation,cathodoluminescence(CL),X-ray fluorescence spectroscopy,Fourier transform infrared spectroscopy,UV-visible sub-photometer,X-ray powder diffraction analysis,electron microprobe analysis etc.The chemical composition mineral composition and rock structure of the olivine basalt and peridotite inclusion can be determined.Based on gem microscope,refractometer,diachroscope and the other conventional gemological testing etc,the gemological parameters of the olivine can be obtained.The olivine basalt of Jiaohe in Jilin province is affected by the Dunhua-Mishan fracture zone.The olivine basalt is alkali trachybasalt in Chuandishan period.The ore contains a large amount of peridotite inclusion,and produces granular output.Deposit is layered structure.The brecciated olivine basalt is gray and black,with cryptocrystalline texture and vesicular structure.The basalt matrix is porphyritic texture.It contains feldspar,olivine,pyroxene and so on.The olivine in basalt matrix has rounder shape granular structure,which is the disintegration of mantle peridotite,rather than basalt phenocrysts.The olivine and pyroxene has undergone alterations of the peripheral which always appears twin crystal and kink band to have compositional band.The core portion of annular mineral reserves the information of mantle mineral composition,while the edge portion has the component being similar to basalt.The element has transference between melt and the host magma.The peridotite inclusion which is beared in the basalt is heterogranular textures.It contains forsterite,enstatite,diopside,chromite and spinel.The peridotite inclusion was named spinel lherzolite.The olivine and enstatite appears twin crystal and deformation lamella.The diopside is emerald green with granular structure.According to the color,the olivine is divided into two kinds.It is speculated that the olivine in different color was formed in different times.Gem grade olivine in Jiaohe of Jilin province is characterized by green to yellowishgreen and transparent to translucent.Olivine internally contains dark solid inclusions,lily pad inclusion,negative crystal,cracks and fissures.It display not distinctive pleochroic color schemes.The average Mohs hardness is Hm 6.52.The average density is about 3.37g/cm3.The sample has a refractive index in the middle of the theoretical value of olivine.Strong absorption occurs in the blue-green region,a clear red-orange region.The peridotite inclusion is mantle-derived xenoliths.It's already there before the magma eruption.It has experienced partial melting.As volcanic activity of the Chuandishan period occurs frequently,the basalt magma which arid the formation mechanism of melting and metasomatism of the mantle fluid rises to the surface with inclusions during basalt eruption,then olivine basalt deposit in the Jiaohe of Jilin province is formed.