Alexandrite is of the Chrysoberyl group
Named after Czar Alexander II. It is one of the most desired gems. It is green in the daylight, and light red in artificial light. This color change is seen best in thicker stones. Alexandrite cat's eye is a great rarity. Care must be taken when working with it as it is sensitive to knocks, not resistant to alkalis, and the color changes when under great heat. It is mined mainly in Sri lanka and Rhodesia. The deposits in Urals are worked out. Further deposits are in Burma, Brazil, Malagasy Republic, Tasmania and the U.S.

• Color : Golden yellow, green-yellow, brown
• Color of streak : White
• Mohs' hardness : 8 1.2
• Specific gravity : 3.70-3.72
• Cleavage : Imperfect
• Fracture : Weak; conchoidal
• Crystal system : Orthorhombic; long prismatic crystals, inter-grown triplets
• Chemical composition : Al2(BeO4) beryllium aluminum oxide
• Transparency : Transparent
• Refractive index : 1.744-1.755
• Double refraction : +0.011
• Dispersion : 0.015
• Pleochroism : Very weak; reddish-yellow, yellow, light green, green
• Absorption spectrum : 5040, 4950, 4850, 4450
• Fluorescence : Usually none
  Green: Weak; dark red