Luster
Pleochroism
Dispersion
Transparency
Refractive Index
Optic Character
Crystal System
Birefringence
Clarity
Weak or absentWalter Schumann
Transparent, Translucent, Transparent to translucent
Transparent to translucent
Strong; X = deep blue or violet; Y = yellow to red-violet or nearly colorless; Z = colorless or very pale blue
Translucent, Translucent to opaque