Gemological And Mineralogical Properties And Color Mechanism Of Larimar From Dominican Republic

Larimar,a rare semi-precious stone,from the Dominican Republic,also known by the trade name Larimar,up till now,it has only been found in Dominican Republic.Its color can range from blue,light blue,bluish green.And white pectolite weave with blue pectolite and green.It appears like the back of a turtle.In most cases,Larimarshows a radical pattern,which implies the pectolitecomes together as a whole.Also,the color zoning differs by the existence of blue pectolite.The main composition of Larimar is pectolite,while some trace elements influencing the color.Our research shows that the physical properties,optical properties and spectroscopic characteristics are in consistent of the chemical composition of pectolite.To identify their gemologicalcharacteristics and the cause of gemological properties.we did some experiment with x-ray diffraction(XRD),UV-visible spectrophotometer(UV-Vis),Fourier transform infrared absorption spectroscopy(FTIR),electron probe micro analysis(EPMA),Inductively coupled plasma mass spectrometry(LA-ICP-MAS),scanningelectronmicroscope(SEM),X-Ray Fluorescence Spectrometer and laser induced plasma spectrometry(LIPS)andso on.The x-ray diffraction(XRD)and Fourier transform infrared absorption spectroscopy(FTIR)shows that the main componentof Larimar is pectolite and few amount of calcite.The Uv-visible spectrophotometer(UV-Vis)shows that the visible region has a distinct broad absorption at the peak of 650?670 nm in the blue and green part of the Larimar,indicating that it might be caused by trace element.Under FTIR,deep blue larimar shows a highest peak at 1055 cm^-1,higher than 994 cm^-1and decrease to 920 cm^-1.Blue pectolite shows a highest peak at 912cm^-1,then decrease from 1050cm^-1to 990cm^-1.While Greenish blue pectolite has almost same appearance but the peaks are weaker.White part only display a strong absorption at470cm^-1.They may come from different phases.And the inclusions are calcite,natrolite and chalcocite.Trace elements in larimar are Cu,Cr,Mn,V,Co,Sr,Pb and etc.In my experiment,the concentration of cooper is 23 to 126ppm,the concentration goes higher as the blue goes deeper.And the concentration of V is 10 to 121ppm in our samples;While V causes the greenish tone.Also,the existence of Mn has some influence in the color of larimar,Mn is a primary element in serandite which causes the pink tone of serandite.The host rock contains magnetite,hematite and other iron oxide,along with calcite,diopside,clay minerals and a large amount of garnet,such as schorlomite,hibschite,and andradite,which are as a result of metamorphism.The appearance of clay minerals,for instance,sepiolite,serpentine and chlorite suggest that the host rock went through strong serpentinization.