The Study On Gemological And Mineralogical Characteristics Of Green Diopside From Three Different Origins

Ordinary gemological properties,spectrum features,and minerological characteristics of the green diopside from three different origins?Pakistan,Russia,Handan in Hebei Province?were analyzed in this thesis through conventional gemological testing methods and modern testing methods.The coloring mechanism,the ore-forming model combined with the geological background and information of paragenetic mineral of the samples are also discussed.These diopside samples from different origins are different in their crystal shapes and surface color,but their conventional gemological characteristics are similar.The data of their refractive index?1.68¹.69?,SG?3.03³.30g/cm³?and mohs hardness?5.76⁷.04?are close to the theoretical value.The ultraviolet visible-near infrared spectrum of samples from Pakistan and Handan,only has the absorption lines caused by Fe^2+/Fe³⁺or Fe²⁺+Fe³⁺.However,the Russian sample has the absorption lines caused by chromium,in band of red wavelength.The scattering peaks in infrared spectroscopy,raman spectroscopy,and result of X-ray Powder Diffraction of these samples are almost the same,which indicates that the kinds of trace elements and its replacement in the crystal structure have little influence on the these three test results.Pakistan Diopside has typical microstructure features--clear grain traces of crystal growth,while the samples from Russia and China are characterized by micro-conchoidal fracture.In the Q-J figure and Wo-En-Fs classification ternary diagram,all samples belong to Ca-Mg-Fe pyroxenes and diopside group.Sample from Russia can be named Chromian diopside,others from Pakistan and China can be named ferrian/ferroan diopside.Inclusions and paragenetic minerals of samples from Pakistan are more obvious,paragenetic minerals include calcite and prehnite;inclusions are composed of quartz,flogopite,chlorite/serpentine,talc and zoisite.The ultraviolet visible-near infrared spectrum test showed that the color machenism of the sample from Pakistan and Handan is mainly determined by Fe²⁺?Fe³⁺charge transfer,but easily affected by transitions of Fe²⁺-Ti⁴⁺and Fe³⁺-O.Meanwhile,the color genesis of the sample from Russia is determined by electronic level transition of Cr³⁺ions in octahedral coordination in the M1 sites.Russian sample has the metallogenic model of pegmatite formed in magmatic crystallization and hydrothermal metasomatism system.Sample from Pakistan are formed in a mining area where acidite or carbonatite rocks were alterated after Regional metamorphic-Contact metasomatism under the influence of hydrothermal process,but 7 samples from Pakistan may be formed in different rock mass,different individual facies at the same mining area,or at different stages in the process of mineralization.Sample from China was formed in diorite or skarn,which protoliths is altered by contact-metasomatism,and the sample was accompanied by the occurrence of the deposit rich in Fe.