热处理宝石级黄色榍石的光谱特征与颜色成因初探

doi:10.3964/j.issn.1000-0593(2024)09-2545-06

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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Ca²⁺、Ti⁴⁺、Si⁴⁺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0.601 wt%）、Al₂O₃（均值0.210 wt%）。中红外反射光谱1 600～400 cm^-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4 000～2 000 cm^-1处可见O—H振动引起的吸收，并伴有3 450 cm^-1为中心的吸收宽带；近红外光谱10 000～4 000 cm^-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Fe²⁺类质同象替代Ti⁴⁺占据八面体位产生Fe²⁺→Ti⁴⁺（IVCT）电荷转移形成的420 nm吸收带，及由O^2-→Fe²⁺和O^2-→Fe³⁺间电荷转移所致450 nm向紫外的强吸收边所致；氧化热处理变棕红是因为部分Fe²⁺变为Fe³⁺，产生Fe²⁺→Fe³⁺（IVCT）所致的540与450 nm向紫外强吸收边的叠加。

关键词：电子探针；红外光谱；紫外-可见光谱；热处理；榍石

Abstract：Sphene is known as titanite, which is a transparent neosilicate mineral that can be used as a gem. Other elements can substitute the cations Ca²⁺, Ti⁴⁺, and Si⁴⁺ 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 0.601 wt%) and Al₂O₃ (average 0.210 wt%). The mid-infrared reflectance spectra 1 600～400 cm^-1are consistent with standard titanite, showing absorptions attributed to O—Si—O and Si—O vibrations. In the mid-infrared transmission spectra 4 000～2 000 cm^-1, the absorption is caused by O—H stretching vibration and accompanied by 3 450 cm^-1 centered absorptions broadband. In the near-infrared transmission spectra 10 000～4 000 cm^-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 Fe²⁺as an isomorphic counterpart for Ti⁴⁺ in the octahedral site, leading to the charge transfer forms of Fe²⁺ to Ti⁴⁺ (IVCT), generating an absorption band at 420 nm. The charge transfer between O^2-→Fe²⁺ and O^2-→Fe³⁺ causes the strong absorption towards the ultraviolet at 450 nm. The brownish-red color after oxidation treatment is attributed to the partial conversion of Fe²⁺ to Fe³⁺, resulting in the overlapping of the strong absorption edge at 540 and 450 nm towards the ultraviolet respectively, caused by the charge transfer forms of Fe²⁺ to Fe³⁺ (IVCT).

Key words：EMPA; Infrared spectrum; Ultraviolet-visible spectrum; Heat treatment; Sphene

收稿日期: 2023-08-23 修订日期: 2024-03-06

中图分类号:

P575.4

基金资助: 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

通讯作者: 岳素伟 E-mail: yuesw@gzpyp.edu.cn

作者简介: 王沛炼，1990年生，广州城市理工学院珠宝学院实验师 e-mail: wangpl@gcu.edu.cn

引用本文:

王沛炼，岳素伟，李嘉妍. 热处理宝石级黄色榍石的光谱特征与颜色成因初探[J]. 光谱学与光谱分析, 2024, 44(09): 2545-2550.
WANG Pei-lian, YUE Su-wei, LI Jia-yan. Spectral Characteristics and Color Mechanism of Heat-Treated Gem-Quality Yellow Sphene. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2024, 44(09): 2545-2550.

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https://www.gpxygpfx.com/CN/10.3964/j.issn.1000-0593(2024)09-2545-06 或 https://www.gpxygpfx.com/CN/Y2024/V44/I09/2545

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