A new X-Ray method to determine the anorthite content and structural state of plagioclases

The possibility of converting a plagioclase into its K-equivalent (Viswanathan, 1970) has given a new simple method to determine its anorthite content. The 4 values of the reflections 201 and 400 in the powder patterns of K-plagioclases vary almost linearly with anorthite content and are practically independent of structural state. Hence either of them or both can be used for the determination of anorthite content. The structural state of acidic plagioclases can be estimated approximately by plotting the 4 values of the lines, 204 and 060, in Fig. 2. This method is particularly useful for determining the anorthite content of plagioclases in fine-grained rocks and synthetic products where other methods including electron microprobe analyser fail.