珍珠层中文石晶体择优取向的XRD极图分析

XRD POLE FIGURE ANALYSIS OF THE PREFERENTIALORIENTATIONS OF ARAGONITE IN NACRE

本文采用XRD极图方法对海水大珠母贝、企鹅珍珠贝及淡水三角帆蚌贝壳珍珠层中文石晶体的结晶学定向进行了研究。根据文石的 ( 0 0 2 )和 ( 0 12 )极图可以推断 ,三种贝壳珍珠层文石的a轴平行珍珠层面 ,c轴垂直珍珠层面。在珍珠层面上 ,二种海水壳珍珠层中文石的a轴亦存在强烈的择优取向现象 ,大珠母珍珠层中文石a轴沿与壳生长纹方向呈 2 0 0°左右的夹角分布 ,企鹅珍珠贝沿近平行壳生长纹的方向分布 ;淡水三角帆蚌珍珠层文石a轴亦平行珍珠层面分布 ,但其择优取向不如海水壳明显 ,在珍珠层面上沿各个角度上均有分布。

The pole figures plotted by X-ray diffraction data are used to analyze the crystalline orientation of aragonite in nacre of Pinctada maxima (Jameson) (PM), Peteria penguin (Roding) (PP) and Hyriopsis cumingii (Lea) (HC) shells. The (002) and (012) pole figures of aragonite indicate that the a-axes of aragonite in nacre of three kinds of shells are distributed along the nacreous layers, whereas the c-axes are all perpendicular to their relevant nacreous layers. The preferential orientation of a-axes of aragonite has also been observed in nacre of saltwater shells, i.e., PM and PP shells. In PP, the a axes of aragonite are nearly parallel to the growing lines of shell, but in PM, there is 20 degree difference between the a-axes and the growing lines of shell. In contrast to PM and PP shells, the a-axes in nacre of HC shells show little preferential orientation.