拉长石晕彩成因的电子探针研究

本文从拉长石晕彩色的空间分布特征研究出发,采用显微镜观察、粉晶X射线衍射及电子探针分析等手段,查明了拉长石不同晕彩区域的结构和成分特征,建立了晕彩拉长石的晕彩色与成分之间的耦合关系,并对拉长石晕彩成因进行了有效的约束。研究结果表明,拉长石的晕彩色是由层状结构对光的干涉所致,其结构单元层由贫钙和富钙两相长石共同组成,当结构层厚度处于128~292nm之间时出现可见光范围内的干涉色,但结构层表面并不绝对平坦,因而出现了有如地形图中等高线似的干涉色。结构层厚度与钙含量有关,随着钙含量的增加,结构层相应地增厚,晕彩色波长也随之增大。但由于产地和结晶环境的不同,干涉色相同的拉长石钙含量不一定相等,但对于同一产地的拉长石而言,干涉色波长与钙含量呈正相关关系。

EPMA studies of iridescence of labradorite

In this paper, the authors used such means as microscope, XRD and EPMA to study the origin and distribution characteristics of iridescent in labradorite. The results indicate that the inner lamellar structure of labradorite causes interference effects which contribute to the iridescent colors. Furthermore, each unit lamellar structure is made up of calc-poor and calc-rich plagioclase feldspar. Only when the thickness of the lamellar structure varies between 128 nm and 292 nm can the interference colors be visible. Because the surface of the lamella is not absolutely smooth, iridescence always looks like the contour line of a map. Additionally, the thickness of the lamella is related to calcic content, i.e., the more the calcic content and the thicker the lamellar, the longer the wavelength of color. The uniform interference color may have different calcic contents, varying from place to place and from environment to environment. Nevertheless, it is demonstrated that the relationship between the iridescence and the calcic content of labradorite is positive at the same place.