马达加斯加硅硼镁铝石的宝石学及谱学特征  

Gemmological and Spectroscopic Characteristics of Grandidierite from Madagascar

作　　者：柏玉林 刘衔宇[1,2] 涂彩 龚雪 陈全莉 BAI Yulin;LIU Xianyu;TU Cai;GONG Xue;CHEN Quanli(College of Earth Sciences,Guilin University of Technology,Guilin 541006,China;Gemological Institute,Shanghai Jian Qiao University,Shanghai 201306,China;Gemmological Institute,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]桂林理工大学地球科学学院,广西桂林541006 [2]上海建桥学院珠宝学院,上海201306 [3]中国地质大学(武汉)珠宝学院,湖北武汉430074

出　　处：《宝石和宝石学杂志(中英文)》2024年第6期15-24,共10页Journal of Gems & Gemmology

基　　金：国家自然科学基金面上项目(41874105);上海建桥学院校级科研项目(BBYQ2104)。

摘　　要：硅硼镁铝石是一种极其罕见的铝硼硅酸盐,产地和产量的有限性使其谱学表征及颜色形成机理研究较少。本文采用常规宝石学测试方法以及电子探针、紫外-可见光光谱、傅里叶变换红外光谱、激光拉曼光谱等测试技术,对马达加斯加宝石级硅硼镁铝石样品的宝石学特征、化学成分及谱学特征进行了系统研究。化学成分分析表明,马达加斯加硅硼镁铝石样品中除主量元素Al、Si、Mg、Fe外,还含有Ca、Mn、Cr、Ti和Zn等微量元素,浅色与深色样品FeO_(T)平均含量分别为0.63%、1.29%,X(X=w_(Fe)/w_((Fe+Mg)))分别为0.024、0.049,X值越大,颜色饱和度越高,多色性色调逐渐加深,多色性强度增大,折射率值与X呈正相关关系。硅硼镁铝石样品的紫外-可光光谱在387、443 nm处特征吸收峰分别为八面体晶体场中Fe^(3+)离子的d—d跃迁^(6)A_(1)→T_(2)^((4D))和自旋禁阻跃迁6A1→(^(4)A_(1g),^(4)E_(g))引起,^(Ⅴ)Fe^(2+)离子在三角双锥结构中的晶体场类似于畸变的八面体配位场,因此458 nm处吸收峰与^(Ⅴ)Fe^(2+)“五态”(6D)和“三态”(3H)分裂项的自旋禁阻跃迁^(5)T_(2g)→^(3)T_(2g)有关,477 nm处吸收峰与^(Ⅴ)Fe^(2+)离子d—d跃迁有关,515 nm处吸收峰为八面体晶体场^(Ⅵ)Fe^(2+)的自旋禁阻跃迁引起,746、771、797 nm和823 nm处吸收峰可能与Fe^(3+)和^(Ⅴ)Fe^(2+)离子之间的Fe^(2+)/Fe^(3+)IVCT有关。红外光谱测试结果显示,400~500 cm^(-1)和630~800 cm^(-1)红外吸收峰分别为[AlO_(5)]+[AlO_(6)]的ν_(4)和ν_(3)振动;530~630 cm^(-1)范围内的吸收为[SiO4]的ν_(4)振动;800~1100 cm^(-1)范围内为硅氧骨干Si-O-Si不对称伸缩振动和硼氧吸收引起;1300~1500 cm^(-1)范围内的吸收带属于[BO_(3)]的ν_(3)振动;3400~4200 cm^(-1)范围内的吸收率与OH的伸缩振动有关。拉曼光谱中1300~1500 cm^(-1)拉曼位移为[BO_(3)]的ν_(3)反对称伸缩振动。Grandidierite is an extremely rare aluminum borosilicate.Due to the limitation of producing area and yield,there are few studies on its spectral characterization and colour formation mechanism.In this paper,the gemmological characteristics,chemical compositions and spectral characteristics of gem-quality grandidierites from Madagascar have been studied in detail using conventional gemmological testing methods,electron microprobe,UV-Vis spectrometer,Fourier transform infrared spectrometer and laser Raman spectrometer.Chemical composition analysis showed that the samples contains trace elements such as Ca,Mn,Cr,Ti and Zn in addition to the main elements Al,Si,Mg and Fe,and the average content of FeO_(T) of light and dark samples is 0.63%and 1.29%,respectively,X(X=wFe/w(Fe+Mg))is 0.024 and 0.049,respectively.With the higher value of the X-ratio,the higher the saturation of the colour,and the intensity of the polychromaticity and the polychromatic hue gradually deepened,the refractive index value is positively correlated with X.The characteristic absorption peaks in the UV-Vis spectra of grandidierite at 387 nm and 443 nm are due to the d—d leap ^(6)A_(1)→T_(2)^((4D))and the spin-barrier leap ^(6)A_(1)→(^(4)A_(1g),^(4)E_(g))of the Fe^(3+)ion in the octahedral crystal field,respectively,^(Ⅴ)Fe^(2+)in the triangular bipyramidal structure resembles the distorted octahedral coordination field,so 458 nm is associated with the spin-barrier leap ^(5)T_(2g)→^(3)T_(2g) for the ^(Ⅴ)Fe^(2+)"five-state"(6D)and"three-state"(3H)splitting terms,and 477 nm is associated with the d—d leap of ^(Ⅴ)Fe^(2+)ions,515 nm is caused by the spin-barrier leap of ^(Ⅵ)Fe^(2+)in the octahedral crystal field,746,771,797 nm and 823 nm absorption peaks may be associated with the Fe^(2+)/Fe^(3+)IVCT between Fe^(3+)and VFe^(2+)ions.The infrared spectra test results show that the infrared absorption peaks at 400-500 cm^(-1) and 630-800 cm^(-1) are theν_(4) andν_(3) vibrations of[AlO_(5)]+[AlO_(6)],respectively;the absorption at 530-6

关 键 词：硅硼镁铝石 颜色成因 紫外-可见光光谱 红外光谱 拉曼光谱 

分 类 号：TS93[轻工技术与工程]