Opal and Sillimanite Optic Character
Opal and Sillimanite optical properties play a significant role while distinguishing these gemstones from each other. These properties are influenced by the Opal Vs Sillimanite like crystallographic symmetry, pleochroism,etc. in the crystal. Some of the optical properties are refractive index, luster, optic character, pleochroism etc. Prominent among these is Opal and Sillimanite optic character. You might have noticed your gemologist rotating the gemstone while testing it. Rotating a gemstone along its optic axis helps in determining its optic character.