Sillimanite and Biotite Optic Character
Sillimanite and Biotite optical properties play a significant role while distinguishing these gemstones from each other. These properties are influenced by the Sillimanite Vs Biotite 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 Sillimanite and Biotite 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.