Alexandrite

Chemistry: Beryllium aluminium oxide, BeAl2O4
Color: Many varities most Varities of green in daylight and red in light
Crystal system: Orthorhombic
Fracture: -
Mohs Scale hardness: 8,5
Refractive index: 1.745 - 1.754
Dispersion: -
Birefringence: -
Pleochroism Present: Strong with Alexandrite
Streak: -
Specific gravity: 3.5 - 3.84

Other:
Alexandrite is the colorchange version of Chrysoberyl, not to confuse with Beryl. Very rare and valuable gem first found in Russia. Green like emerald in daylight and red like ruby incandescent light. The more distinct colorchange the more valuable.