One of the ways to determine the optical sign of a crystal on a universal stage

Abstract

Two provisions are considered: 1. Property of crystals with an angle of optical axes 2V=90°C. 2. Determination of the optical sign of a biaxial crystal on a universal stage, when no optical axis is visible. It is possible to determine the position of the obtuse and acute bisector of the angle of the optical axes, and therefore the optical sign of the crystal.