高品质危地马拉绿色翡翠的红外光谱及拉曼光谱特征

Infrared and Raman Spectral Characteristics of High-Quality Green Feicui from Guatemala

  • 摘要: 翡翠自传入中国以来便深受人们喜爱,是当下中国宝玉石市场上最大宗的玉器产品之一。一直以来,高品质翡翠主要来自缅甸,但由于缅甸国内局势的动荡,加上翡翠矿产资源接近枯竭,高品质缅甸翡翠越来越少。在此背景下,危地马拉翡翠逐渐被开发,陆续进入中国市场。目前已有G. E. Harlow1、何立言2、陈全莉3、徐泽彬4、薛皓予5、甄翠玲6、王礼胜7、邢碧倩8等对危地马拉翡翠的宝石学性质、矿物组成、结构构造和化学成分等进行了研究。然而,危地马拉翡翠颜色丰富,品种多样,成分复杂,前人的研究多针对早期出现在市场上的“蓝水料”“永楚料”或是一些品质一般的灰绿色品种展开。但是,随着危地马拉矿产资源的开发,出现一种被称为“玛雅绿”高端绿色翡翠产品,其品质在一定程度上可以媲美高端缅甸翡翠,已成为翡翠市场上高品质绿色翡翠的重要来源之一。目前对该品质危地马拉翡翠的谱学研究相对薄弱,对这种“玛雅绿”翡翠的认识模糊,检测机构开展有关的工作仍然存在问题。为了解决上述问题,本研究对36颗圆弧状高品质危地马拉绿色翡翠(“玛雅绿”)样品进行了常规宝石学、红外光谱以及激光拉曼光谱测试,系统地研究其谱学特征和矿物组成特征,以期为鉴别来自危地马拉高品质绿色翡翠样品提供重要参考。该类危地马拉翡翠样品呈现鲜艳浓郁绿色,玻璃光泽,质地细腻,少部分样品边缘有极轻微灰色调。在白板上目视观察,透过样品,清晰可见底部刻画线条影像,很难见到内部和外部特征。翡翠样品的相对密度3.27~3.35,平均值3.32,各样品折射率相差不大,均为1.66(点测)。结果表明,高品质绿色翡翠样品的红外光谱在400~1 600 cm-1范围内出现了412、448、524、563、648、885、961、1 070 cm-1处的吸收峰,与绿辉石的主要吸收峰较为一致(图 2),不同翡翠样品的红外光谱相较于绿辉石的标准谱图有轻微偏移,但峰线组合基本不变。拉曼光谱可进行微区分析,且对晶体结构变化引起的振动变化更为敏感。绿色翡翠样品的主要拉曼位移峰为205、375、681 cm-1和1021 cm-1,与绿辉石的拉曼特征峰一致,少部分样品存在点位仍然是绿辉石的拉曼位移峰组合,但其具有向硬玉过渡的特征,可能与Na、Al和Ca,Mg,Fe类质同象替换有关。大多高品质绿色翡翠样品的拉曼谱峰的半高宽较窄且形态尖锐,说明其翡翠结晶度较好。以上测试结果表明高品质玛雅绿翡翠以绿辉石为主要矿物,属于绿辉石质翡翠或硬玉与绿辉石过渡类型的翡翠。

     

    Abstract: Currently, spectroscopic research on high-quality Feicui from Guatemala remains insufficient. In this study, the conventional gemmological methods, infrared spectroscopy, and laser Raman spectroscopy were used to test the 36 high-quality green Feicui samples "Maya green" from Guatemala, to systematically analyze the spectral characteristics and mineral components, and provide critical references for the identification of high-quality Feicui from Guatemala. The infrared and laser Raman spectroscopy results indicate that the characteristic peaks of high-quality green Feicui samples from Guatemala correspond closely with the primary absorption peaks of omphacite. The IR spectra of samples with varying colour grades exhibit slight deviations from standard mineral spectra; however, the overall peak line combinations remain largely consistent. Most samples' Raman spectra match the Raman characteristic peaks of omphacite. A few samples display Raman shift peak combinations typical of omphacite, but with transitional features toward jadeite, potentially due to isomorphic substitutions of Na, Al, Ca, Mg, and Fe. In some samples, the narrow and sharp half-width of the Raman peaks indicate a high degree of crystallization within the Feicui.

     

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