The alexandrite variety displays a color change (alexandrite effect) dependent upon the nature of ambient lighting. Alexandrite effect is the phenomenon of an observed color change from greenish to reddish with a change in source illumination. Alexandrite is a very rare and highly valuable gemstone, and until recently was extremely difficult to obtain due to its rarity

Color Change green to red
Mohs scale hardness 8.5
Specific gravity 3.5 – 3.84
Refractive index 1.745 - 1.754