Optical Properties of Sillimanite are its behavioral responses towards light. While few optical properties can be identified with naked eyes, other require special instruments by the gemologists to identify them. Sillimanite optical properties like luster, clarity, refractive index etc. are used to determine the non-destructive methods during gemstone identification and evaluation.
Sillimanite luster is the quantity of light the crystal reflects when light is incident on it. Sillimanite which is commonly found in Blue, Green, Brownish, Greenish, Colorless, gray color, is Translucent and Transparent in nature. It possess Silky, Subadamantine and Vitreous luster.
Optical properties of a Sillimanite crystal are responsive to the small changes in composition and strain within its crystalline structure. Absolute diligence is therefore necessary during cutting and polishing of the gemstone. All such optical properties are majorly influenced by Physical Properties of Sillimanite.
As we are well aware, refractive index is the phenomenon which is related to bending of light through a medium (crystal). It is used in qualitative analysis of gemstones by gemologists Besides, few gemstones exhibit property of dual refractive indices. This dual nature is known as Birefringence. The value of Sillimanite refractive index is 1.653-1.685. Birefringence value for this gem is 0.020-0.022. So if you are searching for prominent Blue Gemstones, Sillimanite gem is something not miss on, since it has been a favorite pick in the gem wearing community.