陕西旬阳“雨点”绿松石中孔雀石的矿物学特征及颜色环带分析

Mineralogical Characteristic and Colour Zonation of Malachite in "Yudian" Turquoise from Xunyang, Shaanxi Province, China

  • 摘要: 采用拉曼光谱、微区X射线衍射分析和扫描电子显微镜等现代测试手段,对珠宝市场上出现的一种“雨点绿松石”(简称“雨点松”)样品进行测试分析。结果表明,其雨点状区域发育3种不同类型的环带结构,主要差异体现在区域数量、各区宽度及颜色; 微区X射线衍射分析测试显示,雨点状区域的矿物组成为绿松石和孔雀石;拉曼光谱证实其蓝色基底部位为绿松石,绿色部位可见绿松石的拉曼位移(421,644,814,1 041,3 470 cm-1处)和孔雀石拉曼位移(178,1 495 cm-1和3 377 cm-1处);扫描电子显微镜背散射模式观察环带区域,可见绿松石呈柱状、板片状等规则形态, 孔雀石呈粒状、不规则形态充填于规则板状颗粒间; 扫描电子显微镜能谱分析显示,粒状孔雀石中Cu含量达68.67%。综合分析结果显示,环带结构的形成源于绿松石的结晶程度和结构致密程度的差异:结晶程度高,结构致密的绿松石区域,孔雀石含量少且粒径小,环带颜色为浅绿色至蓝色;结构相对疏松的板片状结构绿松石区域,孔雀石含量多且粒径大,环带颜色呈深绿色。

     

    Abstract: A novel type of "Yudian" turquoise samples(turquoise with raindrop-like patterns) obtained from the jewelry market were investigate by a series of modern analytical techniques, including Raman spectroscopy, micro-X-ray diffraction (μ-XRD) and scanning electron microscopy (SEM). The results revealed 3 distinct types of growth ring structures within the raindrop-like pattern areas, distinguished by the number, width, and colouration of the areas they occupy. Micro-area XRD analysis at the growth ring sites confirmed the presence of turquoise and malachite. Raman spectroscopy verified the blue matrix of the growth rings as turquoise, with characteristic peaks at 421, 644, 814, 1 041 cm-1 and 3 470 cm-1. The green regions exhibiting additional Raman shifts at 178, 1 495 cm-1 and 3 377 cm-1, consistent with malachite. Backscattered electron imaging under SEM showed that turquoise displays regular columnar and flaky morphologies, while malachite appears as irregular granular and amorphous aggregates filling the interstices between the turquoise flakes. Energy-dispersive X-ray spectroscopy (EDS) further confirmed that the Cu content in the botryoidal malachite reaches 68.67%. The findings indicated that the growth ring structure represents a symbiotic assemblage of turquoise and malachite. The formation of these growth rings is attributed to variations in the crystallinity and compactness of the turquoise matrix. In regions that turquoise is well-crystallized and densely structured, malachite content is low and its grain size is small, resulting in light green to blue bands. In contrast, areas with a relatively loose flaky structure contain more malachite with larger exposed grains, leading to darker green colouration.

     

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