刚玉中金红石包裹体的结晶学取向研究

发布时间：2018-04-27 15:56

本文选题：刚玉 + 金红石　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：金红石是刚玉中一种常见的包裹体,常呈三组定向排列的针状包体出溶于刚玉中。大量的金红石针会使弧面宝石产生星光效应。本文对金红石在刚玉中的结晶学取向进行了研究并对其成因进行了探讨。本次研究主要采用在宝石显微镜和偏光显微镜,沿刚玉不同的结晶学方向对金红石的形态、大小、排列方向等进行了观察。利用电子探针、傅立叶变换红外光谱以及显微拉曼光谱对金红石针进行了物相分析。同时使用Crystalmaker软件对刚玉和金红石的晶体结构进行模拟,对比其内部的原子排列和原子间距等要素。显微镜下观察显示,金红石以多种形态分布于刚玉中,包括点状、短柱状、“箭状”和丝状等。点状、随形的金红石出现的频率最高,不具有明显定向性,反映出钛分布的无序性。短柱状、“箭状”的金红石针显示明显内凹角,该角度约为111°,与金红石{101}双晶夹角的理论值114°很接近。反射光下金红石针中不同的消光位也揭示了双晶的存在,金红石针的沿长方向与双晶面平行。红外光谱检测出金红石在490-500cm-1区间内有一个特性峰。拉曼光谱检测出金红石特征的610cm-1和448cm-1特征峰。3D晶体结构模拟显示,钛离子与铝离子半径的相似性使得钛可以进入刚玉晶格中,同时不引起明显的晶格畸变。高温下刚玉和金红石的稳定性使得Ti2O3-Al2O3固溶体能够稳定存在。金红石{101}面与刚玉{112__0}面具有明显相似性,原子间距的差异不超过7%。因此,在刚玉{112__0}面中钛以Ti4+-V-Ti4+-VTi4+-V为基本单元对铝(Al3+-Al3+-V-Al3+-Al3+-V)进行取代。Ti还可以Ti O2的形式局部聚集于刚玉晶格中,当温度条件适宜时,可转变为金红石结构析出。金红石针与刚玉的结晶学位置关系为:{101}金红石//{112__0}刚玉,{010}金红石//{0001}刚玉受刚玉生长环境和钛元素来源等因素的影响,钛可以沿刚玉六方双锥面{112__2}晶面富集,出溶后的金红石也会沿该面排列,这类排列方式不受结构的影响。另外,金红石的存在破坏了刚玉晶格的连续性。金红石针的排列方式削弱了刚玉{0001}面的层间力,但对菱面体{101—1}的层间力有一定的加强。这些影响的综合效果是金红石提高了刚玉的硬度。
[Abstract]:Rutile is a common inclusion in corundum. A large number of rutile needles produce starlight effects on curved gemstones. The crystallographic orientation of rutile in corundum was studied and the origin of rutile in corundum was discussed. In this study, rutile morphology, size and arrangement direction were observed by means of gemstone microscope and polarizing microscope along different directions of crystallization of corundum. The phase of rutile needle was analyzed by electron probe, Fourier transform infrared spectroscopy and micro-Raman spectroscopy. At the same time, the crystal structure of corundum and rutile was simulated by Crystalmaker software, and the internal atomic arrangement and atomic spacing were compared. Microscopic observation shows that rutile is distributed in corundum in many forms, including punctate, short columnar, "arrow" and filamentous. The spotted rutile with the shape of rutile has the highest frequency and has no obvious orientation, which reflects the disordered distribution of titanium. The short columnar, "arrow" rutile needle shows an obvious concave angle, which is about 111 掳, which is very close to the theoretical value of 114 掳of rutile {101} double crystal angle. The existence of double crystal is also revealed in different extinction positions of rutile needle under reflected light. The rutile needle is parallel to the double crystal plane along the long direction. A characteristic peak of rutile in 490-500cm-1 region was detected by infrared spectroscopy. 610cm-1 and 448cm-1 characteristic peaks. 3D crystal structure simulation shows that the similarity between titanium ion and aluminum ion radii makes titanium enter corundum lattice without obvious lattice distortion. The stability of corundum and rutile at high temperature enables the Ti2O3-Al2O3 solid solution to exist stably. The rutile {101} face is obviously similar to the corundum {112S _ 0} mask, and the difference in atomic spacing is not more than 7. Therefore, in corundum {1120} plane, Ti is replaced by Ti4 -V-Ti4 -VTi4-V in the form of Al _ 3-V-Al _ 3-V), and TIO _ 2 can also be locally aggregated in corundum lattice, which can be changed into rutile structure when the temperature is suitable. The crystallographic relationship between rutile needle and corundum is as follows: {101} rutile / {112S _ 0} corundum, {010} rutile / {0001} corundum is affected by corundum growth environment and titanium element source, and titanium can be enriched along the hexagonal double cone of corundum {112Snap2}. The dissolved rutile is also arranged along this surface, which is not affected by the structure. In addition, the existence of rutile destroys the continuity of corundum lattice. The arrangement of rutile needles weakens the interlaminar force of corundum {0001} plane, but strengthens the interlaminar force of rhombohedral {101-1}. The combined effect of these effects is that rutile improves the hardness of corundum.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P619.242

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