Mohs Hardness: 6 to 6.5 out of 10
Color: Light to medium-dark bluish purple and violetish blue to violet.
RI: 1.691 to 1.700 (+/-0.005)
Birefringence: 0.008 to 0.013
Optic Character: Biaxial positive
Pleochroism: Strong. Usually strong blue, purplish red and greenish yellow. Sometimes, strong blue, violet and colorless.
Spectrum: Not diagnostic, but you might see bands at 595, 528 and 455nm.
Fluorescence: Generally inert
SG: 3.35 (+0.10 / -0.25)
Routine Treatments: Heating