Crystal system:Orthorhombic
Chemical Formula/composition:BeAl2O4,
Beryllium Aluminum Oxide
Crystal habit:tabular,
heart-shaped
twins, or pseudohexagonal
Hardness:8.5
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.