层状出溶结构导致拉长石晕彩形成——来自透射电镜的证据

Exsolution lamellar structure causes of iridescence in labradorite:evidence from TEM

从拉长石出溶结构的形态特征、成分差异和出溶结构的取向研究出发,采用TEM、STEM以及SAED等手段对其进行测试,发现拉长石出溶结构层的厚度符合理论计算值,结构层的成分由富钙和贫钙两相长石组成,具备了产生干涉作用的必要条件。研究结果表明,拉长石的晕彩色是因其内部的层状出溶结构对光的干涉所致,结构层的厚度主要受富钙相长石的控制。随着钙(An)含量的增加,结构层相应地增厚,且富钙层的增大幅度大于贫钙层,从而导致晕彩色波长也随之增大。出溶结构层的取向为(153),近于平行晶体的(010)面,但不同产地的拉长石,尽管晕彩色相同,其出溶条纹中的钙含量和条纹的具体取向也不尽相同。

Transmission electron microscopy （TEM） and STEM reveal the exsolution lamellar structure in labradorite, which is re-sponsible for the iridescence of labradorite. The labradorite is made up of calc-poor and calc-rich plagioclase, and its thickness is mainly controlled by calc-rich plagioclase. The more the calc content, the thicker the lamellar, and the longer the wavelength of the interference color. Furthermore, the increasing speed of cale-rich plagioclase will surpass that of the calc-poor one. The selected area electron diffraction （SAED） shows that the direction of exsolution lamellar structure is （ 133 ） , which is nearly parallel to （010）. The uniform interference color may have different calc contents and exsolution directions, varying from place to place and from environment to environment.