Morphology and Composition of Fulgurite and Comparison with Similar Natural Materials
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摘要: 闪电熔岩是由于闪电击中地表，瞬间高温使矿物熔融后凝结而成的天然玻璃质岩石.由于标本的稀缺性，国内在该方面的研究几近空白.研究采用CT扫描、三维立体成像技术和电子探针等多种观察仪器，揭示了砂质管状闪电熔岩的内、外部结构特征：玻璃质管壁外表面粗糙且形态复杂，内表面光亮且颜色与外表面不同，管壁内部含大量微小气孔，管道内部可以分为完全贯通、局部堵塞和完全封闭等状态；利用电子探针测定了闪电熔岩的成分：SiO2含量极高，几乎为纯净的玻璃质，仅含有极少量其他金属元素；进一步对比了闪电熔岩、火山玻璃和玻璃陨石在外观、内部结构及成分上的区别，并验证了内蒙古地区类似管状岩石不是闪电熔岩.本研究对闪电熔岩这种罕见的天然物质进行了初步观测，为今后对闪电熔岩更多的科研应用提供基础参考.Abstract: Fulgurites are natural glass material which is formed when lightning strikes and melts the ground and the super high temperature fuses and vitrifies mineral grains. The fulgurite was seldom studied in China due to the rareness of the specimens. By using several new technologies such as CT scanning, 3-D reconstruction of the interior structure and electron probe microanalysis, the results reveal the detailed morphology of both the external and interior structures of the fulgurite as well as its mineral composition. Its external surface is complex and coarse while the internal surface is bright and different from the internal surface in color. The internal surface is full of foramina, and can be classed into three types:fully run-through, partially closed, and completely closed. The fulgurite has the dominant composition of SiO2, with only small proportion of other metal elements. It also was compared with volcanic glass and tektite and determined that a tubular structured stone from Inner Mongolia is not fulgurite. This paper provides some basic data for future study and application of the fulgurite.
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Key words:
- fulgurite /
- volcanic glass /
- tektite /
- tubular structure /
- silicon dioxide /
- petrology
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图 1 样品照片
a.闪电熔岩样品(从左至右，上排依次为S1至S6，下排依次为S7至S12)；b.火山玻璃样品H1；c.玻璃陨石样品B1；d.沙质管状样本G1
Fig. 1. Photographs of the samples
图 2 闪电熔岩样品的高精度CT扫描截面图
a.闪电熔岩样品S1代表竖直贯通管道型；b.闪电熔岩样品S3代表完全封闭管道型；c.闪电熔岩样品S7代表曲折贯通管道型；d.闪电熔岩样品S11代表局部封闭管道型；图像复原图中的4为三维重建图，1、2和3图分别对应蓝色、绿色和红色3个截面)
Fig. 2. Cross section of fulgurite samples by CT
图 3 样品的的形貌像和成分像
a.闪电熔岩S12的形貌像(SEI图像，左)和成分像(BSE图像，右)；b.火山玻璃H1(左)与玻璃陨石B1(右)的成分像(BSE图像)；c.沙质管状样本G1的形貌像(SEI图像，左)和成分像(BSE图像，右，Kf.钾长石，Ab.钠长石，Qtz.石英，Cal.方解石，Ep.帘石)
Fig. 3. SEI (secondary electron image) and BSE (backscattered electron image) of the samples
表 1 雷击石、火山玻璃和玻璃陨石形态成分对比及实验样品测量数据
Table 1. Component comparison of fulgurite, volcanic glass and tektite
雷击石 火山玻璃 玻璃陨石 外形 树枝状，表面附着砂粒 块状，表面洁净，断口呈典型的贝壳状 球状、饼状、哑铃状、泪滴状及不规则状 颜色 灰色、黄白 黑色 黑色 内部结构 中空管状 实体 实体 显微结构 熔融凝固，含大量大型气泡 熔融凝固，含极少量微小气泡 熔融凝固，含极少量微小气泡 SiO2 97% 74% 73% 成分 Al2O3 小于1% 13% 13% 其他 小于1% Na2O：4%、K2O：5%、FeO：1% Na2O：1%、K2O：2%、MgO2%、FeO：4%、CaO：2% 成因 雷击，地表物质高温熔融后凝结 火山熔岩快速凝固 陨石撞击地球，地表物质熔融、飞溅、凝固 
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