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在斜长石类中,钠长石至钙长石的折光率,可随αβ-αn的比率而变化,可是我们要在薄片中精确测定折光率,则往往不甚容易。一般的方法是首先在显微镜下确定切片在晶体中的方位,再测其折光率nγ或nβ或nα的数值,然后按数值去查表,得到所求该长石的种类。这种方法虽能达到测定斜长石的目的,但在操作上有很多的不便,而且如果技术不熟练,所得出的结果,误差往往甚大。现在我们来介绍一种利用折光率测定斜长石的简便方法,这种方法并不是新的发现,以前早就被前人所采用过,但是目前还没有普遍采用及推广,所以现在结合我们的一些体会将它介绍给同志们参考。
In plagioclase, the refractive index of albite to anorthite can vary with the ratio of αβ-αn, but it is often not easy to accurately measure the refractive index in a sheet. The general method is to first determine the orientation of the slice in the crystal under the microscope, and then measure the value of its refractive index nγ or nβ or nα, and then look up the table by the value to get the type of the desired feldspar. Although this method can achieve the purpose of determination of plagioclase, it has a lot of inconvenience in operation, and if the technique is unskilled, the result obtained is often very large. Now we introduce a simple method of using refractometry for the determination of plagioclase, this method is not a new discovery, which has been previously adopted by the predecessors, but there is no universal adoption and promotion, so now with our Some experience to introduce it to comrades reference.