摘要
巴基斯坦Swat矿区祖母绿以饱和绿色和高净度著称,其价格逐年攀升,如何有效鉴别Swat矿区祖母绿的特征成为当前的研究热点。采用常规宝石学仪器、电感耦合等离子质谱、红外光谱、拉曼光谱和紫外-可见吸收光谱对该矿区祖母绿的宝石学及谱学特征进行研究,并探讨其颜色成因。结果显示:(1)Swat矿区祖母绿晶体常为六方柱状,且净度较高。样品颜色呈明亮的绿色,具有中等至强的二色性(黄绿/蓝绿色)。折射率偏高,约1.588~1.599,与晶体碱金属含量高有关。(2)晶体中部分Al与Mg,Fe,Cr等发生类质同象置换。其中替换最多的是Mg元素,含量达11402~12979 ppma(平均为12446 ppma);Fe和Cr元素次之(平均含量分别为2390和2199 ppma)。样品中碱金属元素(Na,K,Rb,Cs)含量很高,总量约14201~16136 ppma,平均为15183 ppma。(3)红外光谱显示指纹区1312,1152,983,838,701,616和559 cm^(-1)处的吸收峰,由[Si_(6)O_(18)]等基团振动所致。近红外区可见较强的Ⅱ型水振动相关吸收峰(7074 cm^(-1)),说明样品中存在较多Ⅱ型水,与晶体中碱金属离子含量较高相符。拉曼光谱显示324,399,516,685和1067 cm^(-1)等祖母绿的拉曼位移,并检测到气液包裹体相关的H_(2)O(3595 cm^(-1))、CO_(2)(1284和1284 cm^(-1))和N_(2)(2327 cm^(-1))以及伴生矿物滑石和磁铁矿的拉曼位移。(4)紫外可见-吸收光谱(UV-Vis)测试结果显示有Cr^(3+)(688~641 nm),V^(3+)(610 nm),Fe^(2+)(860 nm)和Fe^(3+)(375 nm)相对应的吸收峰。样品中Fe元素含量为1124~3561 ppma,Cr元素含量为730~3077 ppma,V元素含量较少,为28.01~263.9 ppma。不同样品中Cr元素含量差距较大,V元素含量差距小,Cr和V离子数比值约3.43~60.05。随着样品颜色饱和度增加,Cr元素含量急剧增大,V元素含量增加极少,Fe元素含量反而降低。推测Swat矿区祖母绿主要致色元素为Cr,其次为V,其色调和荧光可能受Fe元素影响。
Emeralds from Swatin Pakistan are well known for their vivid greenish color and high clarity.How identify the characteristics of emeralds from Swat valley has becomes a hot topicsince their prices have increased every year.Therefore,in this paper,we investigated the gemological andspectral characteristics of emeralds by using conventional gemological tests,LA-ICP-MS,infrared spectroscopy,Raman spectrometer and UV-Vis spectroscopy.Meantime,wealso discussed the color origin of emeralds from Swat.The results show:(1)Most of the rough emeralds from Swat valley are hexagonal-prismsforms.These crystals normally show brightly green and high transpar-ency.There is also a moderate to strong(yellow-green/blue-green)dichroism effect.Most emeralds have a higher refractive index of 1.588~1.599.(2)In the crystals,a part of Al hasbeenreplaced by Mg,Fe or Cr.The most substituted element is Mg,with a content of 11402~12979 ppma(avg.12446 ppma).The second most substitute-ed elementsare Fe and Cr(their average contents are 2390 and 2199 ppma respectively).Concentrations of alkaline cations(Na,K,Rb,Cs)are very high,ranging from 14201 to 16136 ppma(avg.15183 ppma).(3)FTIR spectra show the fingerprint’s absorption peaks at 1312,1152,983,838,701,616 and 559 cm^(-1),caused by the vibration of[Si_(6)O_(18)]groups.The peak at 7074 cm^(-1) is significantly strong,indicating a significantly high quantity of typeⅡH_(2)O in the crystals.It is related to the higher content of alkaline cations(Na,K,Rb,Cs).Raman shifts at 324,399,516,685 and 1067 cm^(-1) are all related to the vibration of emerald.Raman shifts related to H_(2)O(3595 cm^(-1)),CO_(2)(1284 and 1388 cm^(-1))and N_(2)(2327 cm^(-1))are also detected in the gas-liquid inclusions.The associated minerals on crystalsare talc and magnetite.(4)UV-Vis spectra show absorption peaks corresponding to Cr^(3+)(688~641 nm),V^(3+)(610 nm),Fe^(2+)(860 nm)and Fe^(3+)(375 nm).In the samples,the content of Fe is 1124~3561 ppma,the content of Cr is 730~3077 ppma,while the content of V is less,which is 28.01~263.9 ppma.In addition,the content of Cr in different samples changes greatly,the content of V changes little,and the ratio of Cr and V ions is about 3.43~60.05.With the increase of color saturation,the content of Cr increases sharply,the content of V changes very little,and the content of Fe decreases.We can infer that the main chromogenic element of emeralds from Swat valley is Cr,followed by V,while the hue and fluorescence may be affected by Fe.
作者
曹素巧
戴慧
王朝文
于露
左锐
王枫
郭连巧
CAO Su-qiao;DAI Hui;WANG Chao-wen;YU Lu;ZUO Rui;WANG Feng;GUO Lian-qiao(Anhui Geological Experiment Institute(Hefei Mineral Resources Supervision&Testing Center of the Ministry of Land&Resources),Hefei 230001,China;Gemmological Institute,China University of Geosciences(Wuhan),Wuhan 430074,China)
出处
《光谱学与光谱分析》
SCIE
EI
CAS
CSCD
北大核心
2022年第11期3533-3540,共8页
Spectroscopy and Spectral Analysis
基金
国家自然科学基金项目(42072056)
安徽省地质实验研究所科研基金项目(AHDS-2020K09)
安徽省自然资源科技项目(2022-K-12)资助。
