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Optical Anomaly and Sectoral Structure of Minerals

矿物的光学异常和扇形结构

基本信息

批准号：
62540610
负责人：
AKIZUKI Mizuhiko
金额：
$ 1.22万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

项目摘要

Many minerals which grew at a low temperature hydrothermal condition show sectors with abnormal optical properties between crossed polarizers. The origins of the sectors were studied by X-ray and optical methods. The formation mechanisms are explained as follows.In low temperature aluminosilicates such as zeolites and adularia, various Al,Si orderings are produced by electron charge balance between alkali ions and Al,Si atoms on the crystal surface during growth. If Al,Si tetrahedron forms after ulkali ions on crystal surface, the tetrahedron will be preferentially occupied with Al ion. On the other hand, if the tetrahedron forms prior to the alkali ion, it will be preferentially occupied by Si. If growth steps are inclined to mirror plane, Al,Si structure will: be ordered with respect to the mirror, and the mirror will change into twin plane. If the steps are normal to the mirror, the structure will be disordered, and the mirror will be maintained during growth.Also, the ordered arrangements of the Fe^<3+>, Al in garnet and the F,OH in topaz are produced on the side faces of the growth steps because of differences in ionic radii.

许多在低温热液条件下生长的矿物在交叉偏振器之间显示出具有异常光学性质的扇区。通过X射线和光学方法研究了扇区的起源。其形成机理如下：在低温铝硅酸盐如沸石和冰长石中，由于碱金属离子与晶体表面Al、Si原子之间的电荷平衡，在晶体生长过程中产生了各种Al、Si有序结构。如果Al、Si四面体是在铝离子进入晶体表面后形成的，那么Al离子将优先占据四面体。另一方面，如果四面体先于碱金属离子形成，则其将优先被Si占据。如果生长台阶倾斜于镜面，Al、Si结构将相对于镜面有序化，镜面将转变为孪晶面。如果台阶垂直于镜面，则晶体结构将处于无序状态，而镜面在生长过程中得以保持，并且由于离子半径的不同，石榴石中Fe^3+、Al和黄玉中F、OH的有序排列都产生在生长台阶的侧面。