四川凉山联合乡南红玛瑙的宝石学特征及颜色成因探究

Gemmological Characteristics and Cause of Colour of Nanhong Agate from Lianhe Village, Sichuan Province

  • 摘要: 自2009年四川凉山南红玛瑙被发现以后,其凭借产出量高,块度大,颜色好的特点迅速占领珠宝市场。笔者挑选了8块四川凉山南红玛瑙“联合料”样本进行分析研究并探讨了其颜色成因。研究采用常规宝石学测试、偏光显微薄片观察、电子探针、阴极发光及拉曼光谱测试。结果表明,南红玛瑙“联合料”的主要成分为SiO2和FeOT,红色包裹体和隐晶质红色区域的拉曼光谱显示在224、290、410、464、1 318 cm-1处吸收峰,说明FeOT为赤铁矿。赤铁矿包裹体在阴极发光测试下显示红色。南红玛瑙“联合料”为矿物致色,致色矿物并非市场上所说的“朱砂点”,而是赤铁矿,其致色方式有两种:一种为赤铁矿包裹体悬浮于石英中致色,颜色的浓淡与赤铁矿分布的密集程度和矿物颗粒大小有关;另一种是由隐晶质赤铁矿浸染致色。赤铁矿包裹体的尺寸不一,分布不均匀的现象可作为区别其它产地南红玛瑙的特征之一。除此以外,研究显示南红玛瑙的形成是多期次的,赤铁矿包裹体的形成也是多期次的。

     

    Abstract: Nanhong agate from Lianhe Village, was found in 2009,which occupies jewelry market quickly by its unique properties, such as high output, nice colour. In this paper, 8 pieces of agate samples from Lianhe Village were selected to be studied. Test means contain gemmological tests, polarzing microscope observation of section, EPMA, CL and laser Raman spectroscopy. Results indicate that the chemical compositions of Nanhong agate from Lianhe Village are SiO2and FeOT. Raman spectra of red inclusions and aphanitic red area show peaks at 224, 290, 410, 464, 1 318 cm-1, which means FeOTis attributed to hematite.Under CL it shows red light because of hematite.It can be concluded that the colour of Nanhong agate from Lianhe Village is induced by colour-causing mineral. Cinnabar is not the colour-causing mineral, but hematite. The hematite contained in the samples has two kinds of existence forms. One is suspended in quartz and the hue of colour shading depends on the intensity and sizes of hematite.The other existence form is aphanitic hematite in quartz. The phenomenon of hematite with different sizes is a very important characteristics to distinguish Nanhong agate of Lianhe Village from the other mining areas. In addition, the paper shows the formation of Nanhong agate and the hematite inclusion were of multi-phrase.

     

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