黄绿色菱锌矿玉的谱学特征及颜色成因初探

Spectroscopic Characteristics and Coloring Mechanism of Smithsonite Jade

菱锌矿颜色丰富,有黄色、蓝色、粉色、绿色等,矿物学特征及谱学特征的研究较少,对其不同颜色的成因认识亦不明确。选取黄绿色菱锌矿玉,利用X射线粉晶衍射仪、电子探针、激光剥蚀电感耦合等离子体质谱仪、傅里叶红外变换光谱仪、拉曼光谱仪、紫外-可见分光光度计、电子顺磁共振仪等分析显示,样品为纯净的菱锌矿,主要成分为ZnO,其平均含量为61.3%,次要成分有CaO,FeO,MnO,CdO及PbO。样品中含有微量过渡金属元素Fe和Mn,平均含量分别为7363.5×10^(-6)和3558×10^(-6)。样品在740,883和1490 cm^(-1)处出现菱锌矿的特征吸收带,740 cm^(-1)归属于[CO_(3)]_(2-)的面内弯曲振动单峰,883 cm^(-1)属于[CO_(3)]_(2-)的面外弯曲振动峰,1490 cm^(-1)处的强吸收谱带为[CO_(3)]_(2-)反对称伸缩振动所致。拉曼谱有300,728和1091 cm^(-1)等方解石族特征峰,300 cm^(-1)归属于ZnO对称伸缩振动,728 cm^(-1)归属于[CO_(3)]_(2-)面内弯曲振动,1091 cm^(-1)归属于[CO_(3)]_(2-)对称伸缩振动。综合分析认为,Fe^(3+)的^(6)A_(1)→^(4)E(D)跃迁、^(6)A_(1)→^(4)T_(2)(D)跃迁、Mn^(2+)的d电子跃迁产生的紫外-可见光谱377,395和417 nm附近的吸收带是样品产生黄绿色的原因。EPR谱也显示出g=2.0左右的Mn^(2+)的特征六重超精细共振谱线和g=1.98左右的Fe^(3+)的特征谱线。结合样品成分和吸收光谱等特征,可以认为菱锌矿玉样品的黄绿色是由Fe^(3+)和Mn^(2+)的d-d轨道电子跃迁共同导致。

There are few studies on the mineralogical characteristics,spectral characteristics and the cause of color of the Smithsonite jade which appears to take on various hues,such as yellow,blue,pink,green,etc.In this paper,yellow-green smithsonite samples were selected and determined by X-ray powder diffractometer(XRD),electron probe(EPMA),laser denudation inductively coupled plasma mass spectrometer(LA-ICP-MS),Fourier infrared transform spectrometer(FTIR),Raman spectrometer(Raman),UV-Vis spectrophotometer(UV-Vis),electron paramagnetic resonance spectrometer(EPR).XRD test results show that the main component of the sample is smithsonite.EPMA test result shows that the main composition of smithsonite is ZnO,with an average content of 61.3%,and the secondary components are CaO,FeO,MnO,CdO and PbO.LA-ICP-MS test result shows that the content of transition elements Fe and Mn in the samples was relatively high,with an average content of 7363×10^(-6)and 3558×10^(-6),respectively.FTIR spectroscopy analysis showed that there are characteristic peaks of smithsonite,namely 740,883,1490 cm^(-1),which are caused by in-plane bending vibration,out-of-plane bending vibration and antisymmetric stretching vibration CO^(2-)_(3).The calcite Raman characteristic shifts of 300,728,1091 cm^(-1)were shown in every sample caused by the symmetric stretching vibration of ZnO,in-plane bending vibration and symmetric stretching vibration of CO^(2-)_(3).UV-Vis tests show that the absorption bands around 377,395 and 417 nm are caused by the ^(6)A_(1)→^(4)E(D),^(6)A_(1)→^(4)T_(2)(D)transition of Fe^(3+),and d-d transition Mn^(2+)were responsible for the yellow-green color of the samples.The EPR spectrum also shows the characteristic six-fold hyper-fine resonance lines of Mn^(2+)at g=2.0 and Fe^(3+)at g=1.98.Combined with the results above,it is believed that the yellow-green color of the diamond is caused by the electron transition of Fe^(3+)and Mn^(2+)d-d orbitals.