月光石与无色透明拉长石的异同

目前市场上出现了一种无色透明、带有蓝色、橙黄色晕彩的拉长石,外观与月光石十分相似.本文综合了前人研究成果,总结出二者的异同,将这两种长石进行了对比.月光石与无色透明拉长石同属长石族矿物,但分别为两个不同的类质同相系列,在成分上有所区别.无色透明拉长石的折射率与比重比月光石要高;偏光显微镜下月光石呈负低突起,二轴晶负光性,解理少见,不发育双晶,而拉长石则呈正低突起,二轴晶正光性,可见两组交角近90°的解理,聚片双晶发育;月光石中K元素含量较多,而拉长石中Ca、Na的含量则更多;二者的XRD谱线及红外光谱谱线均有较大区别.因此可以通过折射率与比重测试、镜下观察、成分测试及谱学测试来区分月光石与无色透明拉长石.月光效应的形成是由光的散射作用所致,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.

Similarities and Differences Between Moonstone and Colorless Transparent Labradorite

At present, a kind of colorless and transparent labradorite with blue, orange iridescence appears on the market and has a similar appearance to Moonstone. This article intends to find the similarities and differences between them by reviewing previous literatures. Moonstone and colorless transparent labradorite both belong to the feldspar group, but they are of different isomorphism series and have different compositions. The colorless and transparent labradorite has a higher refractive index and specific gravity than moonstone. There are differences in the optical characteristics of moonstone and labradorite observed through a polarizing microscope. In addition, moonstone has constant K contents,while labradorite has constant Na and Ca and their XRD and IR spectrum are also different. Therefore, moonstone and colorless transparent labradorite can be distinguished by refractive index and specific gravity test, features under microscope, compositional and spectrometric analyses. The formation of the adularescence is caused by the light scattering effect, and the labradorescence of the labradorite is caused by the interference of the layered dissolution structure on the light.