A Study On The Gemological Characteristics And Internal Inclusions Of Tourmaline

Tourmaline mineralogical name for the tourmaline,belonging to borosilicate.Its crystal structure and chemical composition is very complex,besides the similar to the same kind of alternative is so broad.The color of tourmaline is very rich due to the changes of formation environmental and the different of trace elements,almost all the color and color combinations can be seen in tourmaline.Tourmaline is not only a single species,but a group.The main mineral species has been identified as 18,such as schorl,dravite,etc.Most of the gemstone tourmaline is elbaite.In this paper,the chemical composition,spectroscopic characteristics and inclusions of different color tourmalines were studied by gemological routine test,gem microscope,polarizing microscope,electron microprobe,infrared spectrometer,laser Raman spectrometer and hot and cold table,also to explore its growth conditions and evolutionary processes.Through the gemological routine test,the selected samples are in good agreement with the optical and mechanical properties of the tourmaline.The relative density of the black tourmaline is higher than others samples.After filling,some samples' relative density is low,and appeared different strength of blue to white and white Fluorescence under ultraviolet fluorescent lamps.The tourmaline after filling treatment can be identifyied by observing surface characteristics and internal characteristics.Through the electronic microprobe test analysis,in addition to a piece of brown tourmaline sample is dravite,the rest are elbaite.The brown-black series tourmaline often not used as a gem because the color is darker and the transparent is not good,so tourmaline is mainly elbaite.Select the different color of the tourmaline for infrared spectroscopy.The results were in accordance with the characteristics of infrared spectroscopy of elbaite.The infrared spectrum also showed the absorption of water vapor,methane and carbon dioxide on the surface of tourmaline.The Raman test of the main minerals,fluid inclusions and solid inclusions of different tourmaline samples,the increase of Fe content will lead to the Raman peak of Si-O stretching vibration and the [OH]-Raman peak in the vicinity of 3590 cm-1,which also suppress the Raman peak near 3650 cm-1 And the presence of Raman peaks in the gas-liquid inclusions indicates that there are CO₂,CH₄ and other gases in the inclusions.The characteristics of the inner inclusions in the tourmaline were observed under polarizing microscope.In addition to needle and tubular inclusions,the other inclusions are smaller,with small number,irregular shape and random distribution.Tubular inclusions are often filled with secondary minerals and gas.The physical and chemical conditions of the ore-forming fluids are as follows: the temperature range is 198 392 ?,the salinity range is 2.41 5.41wt%.The pressure range is 518.6×105Pa⁷22.4×105Pa.Low salinity is consistent with the lower crystallization temperature of tourmaline.