Crystal system:Orthorhombic
Chemical Formula/composition:BeAl2O4, Beryllium Aluminum Oxide
Crystal habit:tabular, heart-shaped twins, or pseudohexagonal
Specific gravity:3.7+
Luster:vitreous or silky
Toughness:good; used in rings
Cleavage: fair in one direction and poor in another
Optics:biaxial positive
Color: yellow, green (sometimes with red spots), red, and brown
Other: Alexandrite changes color when viewed in different lighting, Violet to red in electric light; other colors in natural sunlight including green (most common). Catseye is chatoyant (like tiger's eye).
Varieties: Chryosberyl, Alexandrite (the most valuable), Catseye(cymophane) which has tiger's eye effect,
Localities: Ural Mountains, Russia, Sri Lanka, Brazil, Africa, and Burma
Common simulants: Synthetic corundum (which is a poor imitation) used for alexandrite
Synthetics: Grown by crystal pulling methods and perhaps hydrothermally (not a common synthetic)

Chrysoberyl is the mineral name and is usually found in yellowish green , green, yellow and shades of brown. However, there are several varieties. Along with the common form, there is a cat's eye because of the similarity to the feline's eye. The effect is caused by needle-like inclusions that reflect light into a line of light running along the center of the cut stone. The same effect is seen in fiber optic-glass spheres.
Alexandrite is the most valuable form of chysoberyl. It is rare and has strong change of color depending on the type of light in which it is viewed. In sunlight the color turns almost emerald green, while in incandescent light of a filament bulb it appears a violet-red. An effect that can be seen in sunlight is small flashes of red coming out of the emerald green stone. No other stone is similar to alexandrite.

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