应用XRF－SEM－XRD－FTIR等分析测试技术研究丽水蓝色类欧泊（蛋白石）的矿物学与光学特征

摘要

Opal deposits and their corresponding mineralogical characteristics are rarely reported in China as far as can be ascertained.In the end of 201 3,a type of blue quasi-opal deposit was discovered in Jinyun,Lishui, Zhejiang Province,which has attracted the gem researchers.While the related investigation about this blue quasi-opal has not been reported,in this paper,the mineralogical and optical characteristics of blue quasi-opal collected from Jinyun,Zhejiang Province are carried out primarily by X-ray Fluorescence Spectrometry (XRF ),Field Emission-Scanning Electron Microscopy (FE-SEM),X-ray Powder Diffraction (XRD)and Fourier Transformation Infrared Spectroscopy (FTIR).The results show that the main compositions of blue quasi-opal mineral are silica (95%)and a small amount of Fe2 O3 and Al2 O3 .Meanwhile,an iridescent effect is found on the surface of both unheated and heated samples,which resembles those of natural opals.The XRD spectra with sharp diffraction peak are consistent with those of cristobalite,which is obviously different from some microcrystalline opals (such as Opal-CT,Opal-C)and amorphous opals (Opal-A).In addition,its infrared spectrum shows a typical frequency shift compared with natural opals.As a consequence,these blue ores are preliminary classified as quasi-opals and named as a variant of volcanic-type opals since the geological structure of Jinyun area has the characteristics of Mesozoic volcanic rocks.Based on FE-SEMinvestigation,the iridescent effect is attributed to imbricate structure on ore surface.Further research is needed to confirm their exact category.%直至目前，我国相关欧泊的矿藏及其相应的矿物学特征鲜见报道，2013年末在浙江丽水缙云地区发现的蓝色类欧泊石引起了宝玉石科研工作者的广泛关注，但此矿物的相关研究至今尚未见论述。本文应用X射线荧光光谱（XRF ）、场发射扫描电镜（FE－SEM）结合X射线粉晶衍射（XRD）与傅里叶变换红外光谱（FTIR）等多种综合检测技术首次对该类蓝色原矿的矿物学及光学变彩性质进行研究。结果表明：XRF分析显示蓝色原矿的主体化学组成为 SiO2（质量含量95％），仅含极少量的Fe2 O3与Al2 O3等杂质。同时，蓝色原矿及其相应的热处理后样品局部区域具有明显的变彩特征，主体的化学组成与其光学特征与天然欧泊的组成及变彩效应类同。XRD分析显示原矿粉体的无机相的晶型为方石英相，衍射峰形锐化，该晶体的结构特征明显相异于天然欧泊即微晶类蛋白石（Opal－CT）、Opal－C与非晶类蛋白石（Opal－A）。此外，样品的红外光谱与天然欧泊比较存在一定的频率位移。鉴于此，初步将该类原矿归属为类欧泊，因蓝色原矿所在地丽水缙云地区属于中生代陆相火山岩的地质，因此进一步将该原矿命名为一类火山岩类的类欧泊石，而有关此类欧泊是否可以归属为广义上的欧泊有待商榷。同时基于对蓝色原矿有无变彩效应区域的FE －SEM测试结论，本文初步推测该类矿物的光学变彩特征与原矿表面的“叠瓦状”结构形貌有关。