Gemological Characteristics And Color Mechanism Of Hemimorphite From Xichou Town,Hainan Province,China

Hemimorphite is a kind of very special gem mineral,which is often collected by museums and enthusiasts as gems and ornamental stones.There are high—quality heteropolar minerals in Xichou town of Wenshan Zhuang and Miao Autonomous Region of Yunnan Province,China.Its gemological value is widely valued at home and abroad.In this paper,we will study the basic gemological characteristics,mineral composition,chemical composition,structural structure,crystal structure and spectral characteristics of the hemimorphite ore samples which from the Xichou Town by using modern testing techniques such as conventional gemmological test,UV—Vis spectrum,electron probe,X—ray powder diffraction,infrared spectrum,Raman spectrum,scanning electron microscope,X—ray fluorescence spectrum and reading the previous scholars' research about itThe hemimorphite in this area are lead—zinc deposits.The hemimorphite have kidney structure.The ring structure between blue and white can be seen in the enlarged observation of hemimorphite.The short columnar crystal in the hemimorphite is radially distributed.The hemimorphite grows in layers on the surface of bedrock to form a crust structure.Under the scanning electron microscope,it can be observed that the complete crystal shape is short plate shape;the color is dark blue to white;opaque to translucent;glass—grease luster;refractive index is 1.61—1.63;absorption band appears between 460—500nm measured by grating spectroscope;(110)complete cleavage,(101)incomplete cleavage;relative density is between 3.14g/cm3 and 3.36g/cm3;Mohs hardness is 4—4.5.The absorption peak of 485 nm was measured by UV—Vis absorption spectrum,which was caused by the crystal field transition of Cu and the blue color of hemimorphite.In the infrared absorption spectrum,449.28 cm—1,539.42 cm—1 and 568.04cm—1 absorption peaks due to the bending vibration of Si—O or Zn—O and 609.53,681.07 cm—1 and 934.33cm—1 absorption peaks due to the vibration of silicon oxygen bond will appear.The vibration trend after 1096.0cm—1 and 3632.8cm—1 in the infrared spectrum proves that there is structural water in the hemimorphite;the absorption peaks of 1631.1cm—1 and 3426.8cm—1 prove the existence of crystal water.Among them,the absorption peaks of 1973.1 and 2359.4cm—1 will appear,which can be inferred from the vibration of M—OH impurity metal ions.The characteristic absorption peaks of 333.45cm—1,303.82cm—1,134.73cm—1 and 169.37cm—1 were obtained in the Raman spectrum test.The characteristic absorption peaks of 333.45cm—1,303.82cm—1,134.73cm—1 and 169.37cm—1 appear in the Raman spectrum,mainly due to the stretching vibration and lattice vibration between metal cations Zn—O.he electron probe microanalysis shows that the main component of Xichou town hemimorphite is the oxides of zinc and silicon,containing impurities such as Mg,Fe,Ca,Al,Cr,Cu,Mn,etc.combined with the test of the blue white ring band,it is inferred that copper is the reason that affects the blue depth of hemimorphite.According to the experimental data of X—ray powder diffraction,the cell parameters were calculated: a0=0.8374,nm,b0=1.0719 nm,c0= 0.5120 nm,V0=1.4534 nm.