新疆宝石级锂云母岩的矿物学特征研究

Mineralogical Characteristics of Gem-quality Lepidolite Rock in Xinjiang

  • 摘要: 为了探究新疆一种商业名为“丁香紫玉”材料的宝石学特征及谱学特征,针对5块产自新疆阿尔泰的样品进行了常规检测,采用X射线粉末衍射仪、激光拉曼光谱仪、傅里叶红外变换光谱仪和激光诱导离解光谱仪等仪器测试分析,从矿物组成、拉曼光谱和红外光谱以及化学元素组成进行了研究分析。测试结果表明“丁香紫玉”为宝石级锂云母岩。X射线粉末衍射分析结果表明样品的主要矿物组成为云母,占90%左右,次要矿物钠长石(10%左右)以及微量石英。激光拉曼光谱测试结果显示,其谱峰在高波数3 000~3 800 cm-1。区域有3 628,3 496 cm-1羟基的伸缩振动所致谱峰。红外光谱测试结果,在高波数的羟基伸缩振动吸收带在3 625,3 454 cm-1与拉曼测试的羟基伸缩振动带结果基本相同。激光诱导离解光谱显示样品主要组成元素为H、Li、Na、K、Cs、Ca、Mg、A1、Si,微量元素有Be、Ti、Fe、Mn、Cu、Cr、Hg、Pd等。

     

    Abstract: The gemmological characteristics of gem-quality lepidolite rock in Xinjian are studied, which is called lilac purple jade in Chinese jewelry market. Five samples were investigated by conventional gemmological methods and advanced testing technologies, including X-ray diffraction spectrometer, Raman spectrometer, infrared spectrometer and laser induced breakdown spectroscopy. The testing results show that the refractive index of the sample is about 1.55 (point measurement), and the specific gravity ranges from 2.82 to 2.87. The colour differs slightly from dark purple to light purple, with rare glassy luster. Under gem microscope, a kind of brown inclusion is observed in samples. which distributes like infection.Mineral components were investigated by X-ray diffraction. The main mineral of the sample is mica, which occupies approximately 90%. Minor mineral is albite, which is accounting for nearly 10%, and there is trace amount of quartz (certainly less than 1%).The Raman spectra were characterised by a strong band at 3 628 cm-1 and a relatively weak band at 3 496 cm-1 in high wavenumber region (3 000~3 800 cm-1), which are assigned to OH-stretching modes. The groups of 600-800 cm-1 peak vary in wavenumber and intensity because of the replacement of Si by Al in the tetrahedral. Peaks at 712, 636 and 754 cm-1 are recognized as vibrations of Si-O-Si, Si-0-Al and Al-0-Al. The Raman spectra observed are very similar with the standard spectrum of lepidolite, indicating that the purple jade is mostly consisting of lepidolite.The corresponding infrared spectra showed strong overlapping Si-O-Si modes around 1 010 cm-1 plus less intense bands around 808,751,541 and 481 cm-1. Two overlapping OH-stretching modes can be observed around 3 450-3 650 cm-1,in agreement with a broad band in the infrared spectrum around 3 454 cm-1 and a complex band around 3 625 cm-1 which are in good agreement with the Raman spectra assigned to OH.LIBS results demonstrated that samples were mainly composed of H, Li, Na, K, Cs, Ca, Mg, Al, Si, O,etc. and some trace elements, such as Be, Ti, Fe, Mn, Cu, Cr, Hg, Pd,which accords with conventional chemical composition of lepidolite.

     

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