Iolite and Sillimanite Optical Properties

Iolite

Sillimanite

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1 Optical Properties

1.1 Luster

Vitreous

Vitreous, Subadamantine, Silky

1.2 Pleochroism

Not Available

Colourless to pale brown to yellow

1.3 Dispersion

NANA

0.007 1

1.4 Transparency

Transparent, Translucent, Transparent to translucent

Transparent, Translucent

1.5 Refractive Index

1.52-1.561.653-1.685

1 3.25

1.6 Optic Character

Not Available

1.7 Crystal System

Orthorhombic

1.8 Birefringence

Not Available0.020-0.022

0 0.296

1.9 Clarity

Transparent to translucent

Transparent

Iolite and Sillimanite Optic Character

Iolite and Sillimanite optical properties play a significant role while distinguishing these gemstones from each other. These properties are influenced by the Iolite and Sillimanite Physical Properties 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 Iolite 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.

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Iolite and Sillimanite Transparency

Similar to their colors, Iolite and Sillimanite transparency can also be used as criteria for their primary identification. Although transparency cannot be the only criteria for gemstone identification, it can efficiently used in gemstone grading. Talking about their transparency, Iolite is Translucent, Transparent and Transparent to translucent while Iolite is Translucent, Transparent and Transparent to translucent in appearance.