Lab Alexandrite science
Alexandrite is a variety of the mineral chrysoberyl. What makes Alexandrite different from other varieties of the mineral, such as a cat’s eye, is the presence of not only iron and titanium, but also chromium as a major impurity. This combination of elements results in the green color of the gemstone. Alexandrite can be almost emerald colored, but is more often yellowish green or brownish green. The most prized shades of green of an alexandrite can be described as “emerald, grass, splendid or elegant” and the red shade may be described as “ruby, columbine, garnet, raspberry or fiery.” The more opaque the color, the more expensive the stone. Those stones of a more clear variety are described in color as “dull grass, grayish, opaque, olive or elm- leaf,” while the red shade may be referred to as “murky, cinnamon, Venetian, dull coral, or brownish.”
Alexandrite’s main characteristic is the ability to change color if exposed to a light source that is rich in red rays. This metamorphosis is called Pleochroism. Under such light, such as candlelight, or artificial light, the stone turns red or reddish. This pronounced color change is highly prized. The most valuable alexandrites are brilliant green, and change color to a fiery red under light. The most drastic color changes are the most desirable, as if you were watching a traffic light change color. Usually there is a color bleed through from one color to the other, or there is too much impurity to start with to permit such a drastic color change. Alexandrites from Brazil boast 100% color change, and are therefore the most prized. Because of this color change characteristic, the stone has been called “”emerald by day, ruby by night.” Color change such as this also occurs in sapphire and tourmaline, but alexandrite shows the most dramatic change.
Alexandrite is usually found in sizes smaller than five carats. Sizes over five carats are usually considered large and will command a proportionally higher price. In Ceylon, some of the largest Alexandrites in the world are found, some weighing up to 60 carats each. These stones are of a darker color. Alexandrite is a hard, durable stone, rating an 8 ½ on the hardness scale. It is exceeded in hardness only by the diamond and corundum. It is because of this, and because it is one of the world's most rare gems, that the Alexandrite can be one of the costliest gemstones in the world.
Alexandrites have been found in Russia and in Brazil, though the Brazilian stones do not display as rich a green color as the Russian stones have been known for. They are also found in Sri Lanka, however there as well, the color shades of the stones are not as bright as the Russians. Since the mid 1990’s, Southern Tanzania has been producing alexandrite. It has also been found in Zimbabwe, Burma, India, and Madagascar.
How to Care for Alexandrite
Alexandrite is rated “excellent” for everyday wear however one must still use caution and protect it from harsh chemicals, extreme temperatures and scratches. The best way to clean the stone is with mild dish soap and warm water, using a soft toothbrush.