Alexandrite is the gem variety of chrysoberyl that exibits a
change in color when viewed in different types of light. When viewed
in daylight, alexandrite ranges from a brownish green to an emerald
green color. Under incandescent light, or firelight, it changes to a
brownish to raspberry red color. Although other stones may exhibit
this color changing ability, none are as dramatic as alexandrite.
The red and green coloring is due to a partial replacement of aluminum
by chromium and the ability to change colors is due to the way the
chromium reacts to the blue and red spectrums of light. Natural
alexandrite is seldom found larger than two carats and is often
heavily clouded and included. The largest known alexandrite is a 66
carat Sri Lankan gem currently in the Smithsonian Institute.
Alexandrite is found in the United States and Russia with low-grade
specimens coming from Sri Lanka, Zimbabwe, Brazil, Madagascar, and
Italy. Material with a certificate of Russian origin usually commands
a much higher price on the market. A discovery was made in 1987 near
Hematita, Brazil, that shows a striking color change from raspberry
red to bluish green. Other sources in Brazil, as well as those in
other parts of the world usually show little color change.
| Composition | BeAl22O4 | Class | oxides |
| Specific gravity | 3.68 to 3.75 | Refractive Index | 1.745 to 1.759 |
| Birefringence | weak (.008 to .011) | Pleochroism | strong |
| Cleavage | poor to distinct based on direction | Fracture | conchoidal, brittle |
| Luster | vitreous to greasy | Transparency | transparent |
| Streak | white | Fluorescence | usually none |
| Crystal system | orthorhombic | Twinning | common |
| Hardness | 8.5 | Dispersion | .015 |
| Color | 
Depending on the type of light it is viewed in,
alexandrite will change from green to red. Both colors will often
be muted by brownish tones that will diminish the color change.
The more intense the green and red and the lack of brownish colors
bleeding across the colors, will make a stone more valuable than
one whose colors are muted by brown undertones.
|
| Crystal habit | It forms orthorhombic crystals, generally as V-shaped twins. |
| Other
| Minute replacement of alumina by chromic oxide causes alexandrite's characteristic color change |
Alexandrite was first discovered in 1831 near Ekaterinburg, an
emerald mining region of the Ural Mountains in the Soviet Union.
Alexandrite was named after the Russian Czar, Alexander II,
supposedly having been discovered on the day that he came of age.
As is the case with several other gems, Tiffany Company were very
instrumental during the 1800's in helping this rare gem become very
popular.
Alexandrite is said to enhance a persons self-esteem, bring
happiness and success, and intensify feelings of love and sensuality.
It is also said to be usefull to help treat swollen lymph nodes and
ailments of the spleen, aid pancreatic disorders, as well as treating
of afflictions occurring with leukemia.
