石英岩玉(“独龙玉”)的宝石学及光谱特征

Gemmological and Spectral Characteristics of Quartzite(“Dulong Yu”)

近年来,云南省龙陵珠宝市场出现一种商家声称为“独龙玉”的新兴玉石,因产出量少且面市晚,开发前景可期,但目前尚无相关的宝石学及光谱学特征的研究报道。利用常规宝石学仪器、偏光显微镜、X射线粉末衍射仪、红外光谱仪、拉曼光谱仪、X射线荧光光谱仪、紫外-可见光纤光谱仪等方法对其进行详细的测试分析。结果表明,“独龙玉”主要矿物组成为α-石英和绢云母,石英具细-中粒变晶结构,粒径为0.1~1.4 mm,以小于1 mm的细粒为主,含量高于90%;绢云母具显微鳞片状结构,重结晶特征显著,云母片晶长度最小为0.01~0.02 mm,最大为0.10~0.15 mm,含量为5%~10%,偶尔出现砂粒状锆石包裹体。X射线粉末衍射分析显示含有极少量的碳酸盐类副矿物,包括方解石CaCO_(3)、球霰石CaCO_(3)、碳钙钾石K_(2)Ca(CO_(3))_(2)。X射线荧光光谱及紫外-可见光谱测试表明,其体色由石英晶粒间呈游丝状、鳞片状的绿色绢云母引起,绢云母由Cr、Fe致色,Cr^(3+)离子中的^(4)A_(2)→^(4)T_(2)能级跃迁吸收致630 nm处宽吸收带,Cr^(3+)离子的^(4)A_(2)→^(4)T_(1)能级跃迁吸收及Fe^(2+)-Fe^(3+)离子对间的电荷迁移吸收联合致450 nm处宽吸收带,绿色调深浅与Cr、Fe含量具正相关性。红外透射光谱测试结果显示,2853、2924、2956 cm^(-1)处有强锐吸收峰,以及拉曼光谱显示强的拉曼荧光背景,均证实样品含少量石蜡,不含树脂胶。依据国标GB/T16552-2017《珠宝玉石名称》,该“独龙玉”应定名为石英岩玉,可备注商贸名称:独龙玉或东陵石。

In recent years,a new kind of jade named“Dulong Yu”has emerged in the jewelry market of Longling County,Yunnan Province.Due to the low production and late market entry,the market prospect is promising.However,there have been no academic research report on the gemmological and spectral characteristics of this gemstone.In this paper,the conventional gemmological instruments,polarizing microscope,X-ray powder diffractometer,infrared spectrometer,Raman spectrometer,X-ray fluorescence spectrometer,UV-visible fiber spectrometer were used to carry out detailed testing and analysis.The results showed that the main mineral components of the samples areα-quartz and sericite.The quartz has fine to medium grain crystallized structure,and the particle size is 0.1-1.4 mm,and the content is more than 90%.Sericite has microscopic scaly structure and remarkable recrystallization characteristics.The length of mica crystal is from 0.01-0.02 mm to 0.10-0.15 mm,and the content of mica crystal is 5%-10%.Occasionally,granulation zircon inclusions appear.X-ray powder diffraction analysis showed that it contained very small amounts of carbonate accessory minerals,including calcite,vaterite and fairchildite.X-ray fluorescence spectra and UV-Vis spectra showed that the body colour was caused by green sericite with filamentous and scales between quartz grains.Sericite was colored by Cr and Fe,and the absorption of ^(4) A_(2)→^(4)T_(2) energy level transition in Cr^(3+) ions resulted in a 630 nm wide absorption band.The ^(4)A_(2)→^(4)T_(1) energy level transition absorption of Cr^(3+)ions and the charge transfer absorption between Fe^(2+)-Fe^(3+)ion pairs combined to produce a 450 nm wide absorption band.And there is a positive correlation between the green depth and the content of element Cr and Fe.Infrared transmission spectra showed strong sharp absorption peaks at 2853,2924,2956 cm^(-1),and Raman spectra showed strong fluorescence background,which confirmed that the sample contained a small amount of paraffin and no resin glue.According to GB/T 16552-2017 Gems-Nomenclature,it should be named“Quartzite jade”,and can be noted the market name“Dulong Yu”or“Aventurine quartz”.