红、黑双色火山玻璃的宝石矿物学特征与显微包裹体研究  

A research on the gem-mineralogical characteristics and micro-inclusions of volcanic glass with red and black colors

作　　者：张咪 宋彦军 徐子维 郝森 周蕊恬 许颖 ZHANG Mi;SONG Yan-jun;XU Zi-wei;HAO Sen;ZHOU Rui-tian;XU Ying(School of Gemological and Material Sciences,Hebei GEO University,Shijiazhuang 050031,China;School of Earth Science,Hebei GEO University,Shijiazhuang 050031,China;Gemstone Testing Center of Hebei GEO University,Shijiazhuang 050031,China)

机构地区：[1]河北地质大学宝石与材料学院,河北石家庄050031 [2]河北地质大学地球科学学院,河北石家庄050031 [3]河北地质大学珠宝检测中心,河北石家庄050031

出　　处：《矿物学报》2022年第4期547-554,共8页Acta Mineralogica Sinica

基　　金：国家自然科学基金项目(编号:Z20210005);河北省高校基本科研业务费(编号:QN202232);河北地质大学博士科研启动资金(编号:BQ2018017)。

摘　　要：红、黑双色火山玻璃作为天然玻璃中的少见品种,本文采用常规宝石学测试方法以及扫描电子显微镜(SEM)、红外光谱(FTIR)、X射线粉晶衍射(XRD)、拉曼光谱(LSR)及电子探针(EPMA)对该种火山玻璃的宝石矿物学特征及显微包裹体进行研究。结果显示,红、黑双色火山玻璃点测折射率为1.47,相对密度约2.36,摩氏硬度6~7,具有明显的流动纹理结构并广泛分布有孔径1~2μm的微气孔及因岩浆冷凝收缩所致的纳米级龟裂纹状结构缝隙。样品主体为玻璃态,红色部分含有大量点状及直径约1μm,长度5~25μm的赤铁矿针状包体,黑色部分则含有大量同尺寸的点状及针状磁铁矿包体并使其具明显磁性。此外,样品中还含有约5%斜长石微晶,晶粒尺寸约50~300μm,An约为28.4,另含有极少量尺寸约100μm的锆石包裹体。电子探针测试结果表明,红色及黑色区域玻璃态基质w(SiO_(2))均在75%以上,为典型的黑曜岩类火山玻璃。其中红色区域玻璃基质的w(SiO_(2))平均值为75.517%,黑色区域为77.621%,此外红区在FeO、K_(2)O及Na_(2)O的含量上略高于黑色区域。结合包体形态及电子探针测试结果,我们认为该种黑曜岩的黑色部分为早期酸性程度较高的岩浆冷却析出磁铁矿微晶所致,而红色部分则是磁铁矿在地表或浅层氧化环境下受到后期碱性较高的岩浆接触加热进一步氧化产生赤铁矿所致。As a rare variety of natural glass, the volcanic glass with red and black colors had been scarcely reported in previous studies. In this paper the gem-mineralogical characteristics and micro-inclusions of this volcanic glass has been systematically studied by using conventional gemmological methods, scanning electron microscope(SEM), infrared spectroscopy(FTIR), X-ray powder diffraction(XRD), Raman spectroscopy(LSR), and electron probe microanalyser(EPMA). The results show that the volcanic glass has refractive index of 1.47, relative density of 2.36, Mohs ’hardness of 6-7, obvious flowing texture, widely distributed micro pores with diameters of 1-2 μm, and nanoscale cracks caused by the magma cooling shrinkage. The sample is in typical glassy state. Its red part contains a large number of punctate and needle hematite inclusions with about 1 μm in diameter and 5-25 μm in length. Its black part contains a large number of punctate and needle magnetite inclusions, with similar sizes to those of hematite inclusions, which led to the obvious magnetic property. In addition, the sample contained about 5% plagioclase microcrystal inclusions with grain sizes ranging from 50 μm to 300 μm and the An value of about 28.4, and a few about 100 μm sized zircon inclusions. EPMA results show that the glass matrixes in red and black parts contain over 75% of SiO_(2)(with averages of 75.517% and 77.621%,respectively) which is consistent with that of obsidian volcanic glass. In addition, contents of FeO, K_(2)O, and Na_(2)O of the glass matrix in red part are slightly higher than those in black part. Combining the microscopic morphological characteristics of inclusions with the test results of EPMA, it is believed that the black part of the volcanic glass was resulted from formation of magnetite microcrystals precipitated from the relatively acidic magma in the early cooling stage, while the red part was resulted from the formation of hematite by oxidation of magnetite due to the contact heating of later relatively alkaline

关 键 词：火山玻璃 黑曜岩 红色 黑色 显微包裹体 

分 类 号：P574.2[天文地球—矿物学] P575.4[天文地球—地质学]