The variation of RI with rotation of a doubly refractive gemstone on the refractometer hemicylinder

摘要

The hemicylinder refractometer is used to determine the refractive index (RI) of faceted anisotropic gemstones as a function of crystal orientation. The technique is difficult due to large errors in measurement and uncertainty in the orientation of facets. The theoretical variation is investigated using analytical geometry to generate comprehensive parametric graphs of RI variation. These graphs are analysed systematically, providing methods with reference examples for determining the optic character of anisotropic gemstones.