For multiple choice questions choose the single best answer.
Correct answers are in red.
A gem that has a different refractive index depending on how it is oriented on the polariscope must be isometric. A gemstone with a high critical angle will appear more brilliant than one with a low critical angle, all other factors being equal. To attain maximum return of light from a gem's pavilion facets, they must be cut so the culet angle is 1 or 2 o less than the critical angle for the material. The ordinary and extraordinary rays in a uniaxial mineral are plane polarized. A refractometer can be used to measure refractive indices of any polished gem or mineral.