The optical properties of amethyst quartz

Abstract

Circularly-polarized waves of light, in passing through a section-plate of amethyst quartz, would obviously be retarded unequally in the alternate laminae having right- and left-handed optical activities. Diffraction effects must therefore arise, and these can actually be observed even in almost colourless varieties of the quartz. The section-plate behaves in effect as a phase-change diffraction grating, and the question of the visibility of its structure with and without the aid of polarizers and analysers is discussed in the light of Abbe's theory of microscopic vision.