| Based on searching and reading literature,field exploration and experimental testing,we discussed the geological profile of the "Laoshan Jade" mining area in Shandong province,and studied the samples' gemological characteristics.In order to systematically study their structural characteristics,mineral composition,chemical composition,and spectral characteristics,a lot of testing methods were used,such as Polarizing Microscope,Scanning Electron Microscope(SEM),Electron Microprobe Analysis(EMPA),Fourier Transform Infrared Spectrometer(FTIR),Raman Spectrometer and X-Ray Fluorescence Spectrometer(XRF).Those results provide sufficient data for exploring the formation and evolution of "Laoshan Jade"."Laoshan Jade" is green to dark green,with waxy luster as a whole and silk luster in part.It is slightly transparent to opaque.The Refractive index is 1.560-1.568.Mohs hardness is 4.45-5.20 and the average relative density is 2.56-2.71.The jade has micro-flaky,scaly,fibrous and granular blastic texture,blocky structure and banded structure.It belongs to serpentine jade.Under the Polarizing Microscope,it can be seen that the main mineral is serpentine,and the minor mineral is chlorite.Some samples also have magnesite,olivine and pyroxene as minor minerals.The accessory minerals are ferrous metal minerals.Therefore,the “Laoshan” jade can be named as serpentine rock.The EMPA results show that the main component of the sample is antigorite,which is mainly altered from olivine.Chlorite is mainly penninite and clinochlore,with formation temperature being about 200 ?,which is altered from pyroxene.The spinel minerals are magnetite and chromite.The magnetite has a metamorphic origin.The chromite has different zonation.Its core has a magmatic origin,with average temperature and pressure being calculated to be 1348 ? and 3.1 GPa.The projection results show that it comes from the depleted mantle peridot near the subduction zone.The edge of chromite has metamorphic origin and its formation temperature is lower than 500 ?.The olivine in some samples,which are residual minerals from the original rock,belongs to forsterite and chrysolite.Its projection shows that it comesfrom the mantle peridotite.Most of the remaining pyroxene is diopside and has not been completely altered.Infrared spectrum shows that the main mineral of the sample is serpentine.There are some peaks of carbonate minerals,too.Raman spectrum shows that serpentine is mostly antigorite,with a small amount of lizardite.In addition,other minerals such as chlorite,magnesite,magnetite,olivine and pyroxene have also been identified,which is consistent with the results of EMPA and microscopic identification.The results of the major elements in the whole rock show that the overall ignition loss of the rock is very high,and the samples have experienced deeper serpentinization.The projection results show that the rock belongs to metamorphic peridotite.Its composition is relatively rich in Mg compared to the original mantle peridotite,and more deficient in fusible components(Al,Ca),which indicate that the original rock of serpentinite has undergone a certain degree of partial melting.The overall analysis shows that "Laoshan Jade" is serpentine jade.It's petrology name is serpentine,and the original rock is a partially melted peridotite near the mantle wedge of the subducting continental crust plate,which reacts with the fluid brought by the subduction zone.The pyroxene erodes into chlorite,the olivine is altered into serpentine and the magnetite is formed.The edge of the chromite in the original rock is altered into magnetite by the iron-rich fluid.Finally,the original rock is transformed into serpentine. |
PDF Full Text Request