Composition and Formation of Octahedral Inclusion in Spinel
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摘要: 目前对于尖晶石内部八面体包裹体的成分，宝石学研究中尚存在争议。基于市场上尖晶石主要产地为缅甸且八面体包裹体为缅甸及斯里兰卡产地的特征包裹体的两方面考虑，对收集到的52粒主要产地为缅甸的尖晶石样品进行观察，据包裹体存在的共性及包裹体所处位置选择较有代表性的4颗宝石级尖晶石样品进行显微观察和拉曼光谱测试。拉曼光谱显示包裹体有位于155、282、712、1 086 cm-1的方解石拉曼峰和位于177、300、1 099 cm-1的白云石拉曼峰。通过对八面体包裹体分布特征的观察，从突起、空间分布、偏光特点和成分等方面分析，得出结论：缅甸尖晶石内部的包裹体若呈白色或无色、边界清晰、定向排列、八面体形状，则可以判断他们是由残余成矿热液白云石或方解石所充填的同生、次生或假次生负晶包裹体。但由于研究样品数量和来源的局限性，对于其他尖晶石族矿物作为八面体包裹体的存在缺乏相关证据，有待进一步验证。Abstract: At present, there isn't any reasonable conclusion towards the composition of octahedral inclusions in gemmology, and some of the existing opinions are not supported by credible evidence. Therefore, it is necessary to review the available opinions with further evidence. To solve this question, the authors conduct this study based on spinels primarily from Burma with the characteristic octahedral inclusions seen in spinels from Burma and Sri Lanka. After observing 52 pieces of spinels from Burma, the authors chose 4 representative pieces for microscopic observation and laser Raman spectroscopy to find out the composition and formation of octahedral inclusions. From the Raman spectra of the inclusions, 155, 282, 712 and 1 086 cm-1 peaks of calcite and 177, 300, 1 099 cm-1 peaks of dolomite were seen. The spatial distribution of the inclusions can provide some evidences of their formation. The authors draw conclusion from its refractive index, special arragenment of the inclusions, polarity and composition that the octahedral inclusions in spinels from Burma have the following features:white or colourless, sharp border, directional alignment, etc., usually indicating that they are syngenetic, secondary or pseudo-secondary negative crystals filled with dolomite or calcite from residual metallogenic hydrothermal solution. However, considering the limit of the researched sample numbers and sources, the existence of other spinel group minerals as octahedral inclusion is not verified in the papers and it needs further work.
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Keywords:
- octahedral inclusion /
- spinel /
- negative crystal /
- Raman spectrum
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