Research On Mineralogical Characteristics Of Jiaohe Olivine Of Jilin

Jiaohe olivine of Jilin province is one of two major mining area.in China. The author takes the olivine of Jiaohe Dashihe in Jilin province as the research object. The research is based on laboratory analysis via hand specimen observation, conventional gemological testing, 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 gemological parameters can be obtained. The chemical composition mineral composition and rock structure of the olivine basalt can also be determined.Gem grade olivine is short columnar or granular. Its crystal is clean and transparent which has the polished surface with glass luster and the fracture with oil sheen. Its color is characterized by olive green to yellowish green. The color of the mineral deepens with the color of the sample. Strong absorption occurs in the blue-green region, a clear red-orange region which are origin characteristics by780 nm, 635 nm and 489 nm. The sample has a refractive index of 1.65 to 1.69, a density of about 3.33 ~ 3.39 g / cm3. The average Mohs hardness is Hm 6.38.Olivine internally contains brown-red spinel, dark green diopside, chromite dark solid inclusions, fluid inclusions filling along cracks and fissures, disseminated.trace of iron, etc.Brecciated basalt bearing olive-inclusions is gray and black, with dense block or vesicular structure. It contains different sizes of angular, rounded shape peridotite xenoliths with a size range in 2-10 cm and an erratic distribution. The peridotite has clear boundaries with the basalt, it also has a coarse-grained structure, and a mineral composition with more than 50% olivine, 20% to 30% of pyroxene, a small amount spinel, chromite and other dark minerals. It has a mineral combination of forsterite,enstatite, diopside, spinel, chromite, spinel and lherzolite.The basalt matrix were observed via microscope, which is shelf-like feldspar crystal packing, filled with vitreous, olivine, pyroxene microcrystalline and magnetite,etc. The structure is a transition of intersertal texture- tholeiitic texture- intergranular texture. The peridotite has original granular texture. The crystal is under stress and the fracture is widely developed, so that kink band appears and partly replaced by iddingsite. In the basaltic matrix, part of olivine crystals with large particles are xenocrysts which is the disintegration of mantle peridotite, rather than basalt phenocrysts. Xenocryst rapid reacts with high-temperature melt. Some large particles olivine, spinel appears to have compositional band. some minerals with small particles react completely, leading to the banding disappearance. 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 olivine composition is forsterite to Peridot. Evolution equation is(Mg, Fe)2SiO4(forsterite) + melt(original magma) =(Mg,Fe)2SiO4(chrysolite) + melt(evolved magma). The element transference between melt and xenocryst is one of the evolution of lithospheric mantle component, resulting in the disappearance of the palaeomantle.