Optische Charakterisierung von zwischen Hoch- und Tieftemperaturform gelegenen Übergangsstadien bei Plagioklasen

Abstract

A method is described whereby the optical orientation of plagioclases may be numerically described with the aid of three independent parameters (Euler-angles). An examination of their variation relative to the anorthite-content leads to an exact characterization of the high- and low-temperature optics, as well as of intermediate stages in which Si and Al are only partially ordered. It seems likely that such stages are considerably more frequent in nature than has hitherto been supposed.