拉曼面扫描无损鉴定矿物包裹体：以彩虹方柱石中的磁铁矿包裹体为例

如何利用拉曼光谱对矿物中的微小包裹体进行无损鉴定，是矿物学与宝石学研究中经常遇到的问题。彩虹方柱石是一种含有特殊包裹体的方柱石，其包裹体在反射光下呈现虹彩效应。本文利用超景深显微镜、电子探针、显微激光拉曼光谱、X射线粉晶衍射分析，特别是创新性运用拉曼光谱面扫描填图技术对彩虹方柱石中微小的磁铁矿包裹体进行了无损鉴定研究。显微特征显示，彩虹方柱石的包裹体可能和固溶体出溶有关，微小包裹体平行排列，形成了类似反射型衍射光栅的结构，导致其在反射光下出现彩虹色。根据电子探针测试结果，彩虹方柱石端元组分为Ma_68.2-69.7Me_30.3-31.8，属针柱石亚族。根据拉曼光谱测试结果，部分包裹体出现了位于661 cm-1处的弱拉曼峰。由于图谱信噪比普遍偏低且该峰并不会在所有测试位置出现，所以容易被忽略。为进一步探究该峰的来源，对包裹体部位进行拉曼面扫描，并选择630～680 cm-1范围的拉曼峰进行了相关性分析，确认了包裹体位置普遍存在位于661 cm-1处的弱拉曼峰。该拉曼峰可归属为磁铁矿的A_1g振动峰，从而确认了产生虹彩效应的针状包裹体中包含有更微小的磁铁矿包裹体。XRD测试结果表明，包裹体较多的样品存在位于2.51 Å处的磁铁矿（311）晶面衍射峰，进一步验证了拉曼光谱面扫描的结果。根据上述实验，拉曼面扫描技术或许可以成为鉴定矿物宝石中微小包裹体的有效辅助性手段。该研究创新性提出，如果矿物包裹体的拉曼信号很弱，可以将拉曼面扫描结果与包裹体的分布特征结合分析来判断该信号的有效性。同时为无损鉴定矿物中的包裹体提供了一种新的研究思路与方法。

Nondestructive Identification of Mineral Inclusions by Raman Mapping: Micro-Magnetite Inclusions in Iridescent Scapolite as Example

Using Raman spectroscopy to nondestructively identify tiny inclusions in minerals is a significant problem in mineralogy and gemology. Iridescent scapolite is a kind of scapolite with special inclusions. Its inclusions present various spectral color under reflected light. In this research, magnetite inclusion in iridescent scapolite was nondestructively identified by hyperfield microscope, EPMA, Micro-Raman Spectrometer and XRD. Raman spectroscopy mapping technology was innovatively used. The microscopic characteristics indicate that the inclusions may be related to solid exsolution. The tiny inclusions grow parallelly and form a structure that is similar to the reflection grating, leading to iridescence under reflected light. The results of EPMA show that the end-member composition of iridescent scapolite is Ma_68.2-69.7Me_30.3-31.8, belonging to the dipyre subgroup. According to Raman spectra of some inclusions, there is a weak peak at 661 cm-1. This peak, which does not appear in all testing locations, is easy to be ignored due to the low signal-to-noise ratio. In order to further study the assignment on this peak, the Raman mapping testwas carried out, and the mapping image was made based on the relative intensity of the peak range at 630～680 cm-1. The result confirmed that the weak Raman peak at 661 cm-1 appeared in most of the inclusion positions. This Raman peak can be assigned to the vibration mode A_1g of magnetite. Then we confirmed that the needle-like inclusions with iridescent effect contained smaller magnetite inclusions. According to the results of XRD, a diffraction peak at 2.51 Å, which belongs to the (311) crystal surface of the magnetite. It was detected in the sample containing many inclusions. It also furtherpro of the Raman mapping results are credible. According to the above experiments, Raman mapping technology may be an effective auxiliary means to identify tiny inclusions in minerals and gemstones. This study innovatively proposes that if the Raman signal of inclusions in minerals is weak, the effectiveness of the signal can be judged by combining the Raman mapping results with the distribution characteristics of inclusions. At the same time, it provides a new research idea and method for the nondestructive identification of inclusions in minerals.