缅甸“咖啡色”石英质玉的呈色机理  

Study on coloring mechanism of coffee color quartzite jade from Myanmar

作　　者：余炼钢 YU Liangang(Dehong Teachers′College,Dehong 678400,China)

机构地区：[1]德宏师范高等专科学校,云南德宏678400

出　　处：《超硬材料工程》2023年第2期52-56,共5页Superhard Material Engineering

基　　金：2023年云南省教育厅科学研究基金项目(2023J1710)。

摘　　要：近年来云南龙陵珠宝市场上流行一种来自缅甸的“咖啡色”石英质玉石品种,其质地细腻,颜色饱和均匀,呈深褐色、深灰褐色、褐色、浅黄褐色等系列变化,显著特征是褐色中带深浅不同的绛紫色调。运用岩矿薄片鉴定、红外光谱、X-射线荧光光谱、紫外-可见光谱等方法对其矿物组成及结构、化学成分及谱学特征进行测试分析,重点探讨其呈色机理。岩矿薄片鉴定及红外光谱测试显示该玉石由纯度极高的α-石英构成,呈细粒状-纤维状变晶结构,晶粒尺度以1~10μm为主,少部分为10~20μm,极少部分为20~50μm,属于隐晶质玉髓范畴。红外光谱在1890、3129、3440 cm^(-1)处吸收峰指示其显微结构空隙中存在自由水。X-射线荧光光谱分析显示SiO_(2)质量分数在99.6%以上,同时含Cl、K、Ca、Ti、Fe、Ni、Zn多种微量杂质元素。551 nm处紫外-可见吸收峰由Fe吸收引起。综合化学成分及紫外-可见光谱特征推测,其颜色产生与Fe、Ni、Ti相关,以Fe为主,Ni为辅,Ti的影响较小。Fe、Ni、Ti以类质同像替代Si进入石英晶格,形成空穴色心[FeO_(4)]^(4-),同时部分Fe^(2+)与Ti^(4+)离子间发生Fe^(2+)+Ti^(4+)→Fe^(3+)+Ti^(3+)电荷迁移,以及Ni^(2+)离子内部d-d电子跃迁,三种机理对可见光的吸收及不同程度叠加的综合作用是形成该玉石独特的“咖啡色”系列颜色的原因。In recent years,a new quartzite jade of coffee color variety from Myanmar is popular at Longling jewellery market in Yunnan Province.It is characterized by dense and delicate texture,and brown color with purplish tint.It is dark brown,dark gray brown,brown,light brown and other series of colors.In this paper,infrared spectroscopy,UV-visible spectroscopy,X-ray fluorescence spectroscopy,and mineral and rock identification of thin section are used to study its mineral constituent and structure,chemical composition,spectral characteristics,and the mechanism of color formation is also discussed emphatically.Mineral and rock identification of thin section and infrared spectrum test show that this kind jade is composed ofα-quartz with high purity,with fine granularity and fibrous morphocrystalline structure.It has a fine granularity and fibrous texture,the grain size is mainly 1-10μm,a few of 10-20μm,and a few of 20-50μm,belonging to the cryptocrystalline chalcedony.The absorption peaks at 1890 cm^(-1),3129 cm^(-1) and 3440 cm^(-1) in infrared spectroscopy indicate the presence of free water in the microstructural voids.X-ray fluorescence spectra shows that the mass fraction of SiO_(2) is more than 99.6%,and the trace impurity elements of Cl,K,Ca,Ti,Fe,Ni and Zn are also contained.The UV-visible absorption peak at 551 nm is caused by Fe element.Based on the chemical composition and UV-Vis spectral characteristics of the samples,it can be inferred that the jade color is produced by Fe,Ni and Ti element.Fe is the main effect,Ni is the second one,and Ti has little effect.Fe,Ni and Ti elements enter the quartz ctystal lattice through isomorphous replacement of Si,forming vacancy color centers[FeO_(4)]^(4-).Meanwhile,charge transferring Fe^(2+)+Ti^(4+)→Fe^(3+)+Ti^(3+)occurs between Fe^(2+)and Ti^(4+)ions,and d-d electron transition occurs inside Ni^(2+)ions.The absorption of visible light by the three mechanisms and the combined effect of different degrees of superposition are the reason for the formation of the unique

关 键 词：石英质玉 咖啡色 结构特征 化学成分 呈色机理 

分 类 号：TS933[轻工技术与工程]