热处理宝石级黄色榍石的光谱特征与颜色成因初探  

Spectral Characteristics and Color Mechanism of Heat-Treated Gem-Quality Yellow Sphene

作　　者：王沛炼 岳素伟 李嘉妍 WANG Pei-lian;YUE Su-wei;LI Jia-yan(School of Jewelry,Guangzhou City University of Technology,Guangzhou 510800,China;Jewelry Institute,Guangzhou Panyu Polytechnic,Guangzhou 511400,China)

机构地区：[1]广州城市理工学院珠宝学院,广东广州510800 [2]广州番禺职业技术学院珠宝学院,广东广州511400

出　　处：《光谱学与光谱分析》2024年第9期2545-2550,共6页Spectroscopy and Spectral Analysis

基　　金：国家自然科学基金项目(41403032);广东省普通高校特色创新类项目(2022KTSCX184)资助。

摘　　要：榍石是钙钛岛状硅酸盐矿物,晶莹剔透者可作宝石,其中Ca^(2+)、Ti^(4+)、Si^(4+)可被其他元素所替代。选取黄色榍石进行热处理,结果显示样品在700℃及以上的氧化气氛中加热,变为棕红色,还原气氛再次加热可褪回黄色。电子探针成分分析显示,样品成分与标准榍石成分一致,含少量FeO(均值0.601wt%)、Al2O3(均值0.210wt%)。中红外反射光谱1600~400cm^(-1)与标准榍石一致,可见由O—Si—O和Si—O振动引起的吸收;中红外透射光谱4000~2000cm^(-1)处可见O—H振动引起的吸收,并伴有3450cm^(-1)为中心的吸收宽带;近红外光谱10000~4000cm^(-1)处可见O—H振动引起的吸收。紫外-可见吸收光谱显示,榍石样品(未加热)的黄色是Fe^(2+)类质同象替代Ti^(4+)占据八面体位产生Fe^(2+)→Ti^(4+)(IVCT)电荷转移形成的420nm吸收带,及由O_(2)^(-)→Fe^(2+)和O_(2)^(-)→Fe^(3+)间电荷转移所致450nm向紫外的强吸收边所致;氧化热处理变棕红是因为部分Fe^(2+)变为Fe^(3+),产生Fe^(2+)→Fe^(3+)(IVCT)所致的540与450nm向紫外强吸收边的叠加。Sphene is known as titanite,which is a transparent neosilicate mineral that can be used as a gem.Other elements can substitute the cations Ca^(2+),Ti^(4+),and Si^(4+)in sphene.Yellow sphene was selected for heat treatment to explore the heat treatment process of sphene.The results showed that the yellow sphene samples were heated in an oxidizing atmosphere at 700℃and turned brown-red above,whereas,the reducing atmosphere heated again to turn yellow again.The composition analyzed by the electron microprobe analysis(EMPA)shows that the samples are consistent with the standard sphene composition,and also contain a small amount of FeO(average 0.601wt%)and Al2O3(average 0.210wt%).The mid-infrared reflectance spectra 1600~400cm^(-1)are consistent with standard titanite,showing absorptions attributed to O—Si—O and Si—O vibrations.In the mid-infrared transmission spectra 4000~2000cm^(-1),the absorption is caused by O—H stretching vibration and accompanied by 3450cm^(-1)centered absorptions broadband.In the near-infrared transmission spectra 10000~4000cm^(-1),the absorption is caused by O—H stretching vibration.The UV-visible absorption spectrum illustrates that the yellow color of the untreated titanite sample is due to the substitution of Fe^(2+)as an isomorphic counterpart for Ti^(4+)in the octahedral site,leading to the charge transfer forms of Fe^(2+)to Ti^(4+)(IVCT),generating an absorption band at 420nm.The charge transfer between O_(2)^(-)→Fe^(2+)and O_(2)^(-)→Fe^(3+)causes the strong absorption towards the ultraviolet at 450nm.The brownish-red color after oxidation treatment is attributed to the partial conversion of Fe^(2+)to Fe^(3+),resulting in the overlapping of the strong absorption edge at 540and 450nm towards the ultraviolet respectively,caused by the charge transfer forms of Fe^(2+)to Fe^(3+)(IVCT).

关 键 词：电子探针 红外光谱 紫外-可见光谱 热处理 榍石 

分 类 号：P575.4[天文地球—矿物学]