Alexandrite changes color from green in daylight to red in incandescent light. The first time you see it, it is hard to believe your eyes!  Alexandrite was first discovered in Czarist Russia, in the Ural mountains, in 1830.  Since the old Russian imperial colors were red and green it was named after Czar Alexander II on the occasion of his coming of age.  Genuine Alexandrite is one of the world's rarest and most coveted Gemstones, it's so rare that most people have never even seen one.  Alexandrite is in the Chrysoberyl mineral family and is one of the most fascinating gemstones throughout history.  A color change occurs in very few gemstones.  Alexandrite is highly prized, and, as always, the exact tone of the color is an important factor in it's value, the most expensive being brilliant green turning to very red.  The natural color change in Alexandrite ranges from various shades of Green (blue-greens, kelley-greens, olive-greens, teal-greens, etc.) when the gem is under "fluorescent" lighting, or in natural outdoor light "in the shade" (not direct sunlight)... then the color changes to various shades of Red (burgundy-reds, purplish-reds, reddish-purples, violetish-purples, amethyst, etc.) when exposed to light in a room with only incandescent light, tungsten light, or candlelight (a flashlight will bring out the color change too).  To get the maximum color change effect the gem is best viewed in a dark room with no outdoor light at all, then turn on a fluorescent light to see the green shade, then turn on a standard incandescent light bulb with the fluorescent light off to see the reddish shade.  You can cycle the lights back and forth to see the distinct color change.  Alexandrite will normally darken when taken out into direct sunlight, since it is subjected all the colors in the spectrum,  also if subjected to several types of lighting sources at the same time the colors may twinkle with both the red and the green color bouncing around different facets in the stone.  When the primary color has a bit of brownish in with the green, this is due to the bleeding of the two colors.  Typically this is referred to as the percentage of color change.  The higher the color change percentage, the more expensive the gem. 
When the color change from fluorescent light to tungsten light is not an obvious color change from one of the various shades of green to one of the shades of red, the gem is usually called "alexandrite like" or a "color change Chrysoberyl" since it does not quite have the distinct greenish to reddish color change to be called "Alexandrite".
Alexandrite can be found in jewels of the period as it was well loved by the Russian master jewelers. Master gemologist George Kunz of Tiffany was a fan of alexandrite and the company produced many rings featuring fine alexandrite in the late nineteenth and early twentieth century, including some set in platinum from the twenties. Some Victorian jewelry from England features sets of small alexandrites.  Russian Alexandrite is extremely rare, the original source in Russia's Ural Mountains has long since dried up after producing for only a few decades.  A few Russian miners are still working those trailings there in the Urals, and they are finding a few fine gems, but only in very limited quantities.  We secure these rare Russian gems as soon as they are found and made available to us.  Most are small stones, less than a carat, but they all have a dramatic color change.  We are happy to be able to make these beautiful rare gemstones available to you.   Material of Russian origin like this is particularly valued by collectors.  We also have some of the finest alexandrite from Brazil, a locality called Hematita.  This Brazilian alexandrite find was made in 1987 and some of these gems show a striking similarity to the fine Russian gems having an attractive color change from bluish-green to raspberry like purplish-red.  The Brazilian gems are also in limited quantities, so they remain extremely rare and expensive, but we are able to get them in larger stones over a carat and make them available to you.  The production of this new material means a new generation has the opportunity to own this beautiful and rare gemstone.  We also have top Ceylon alexandrite with very good color change, it is not quite as dramatic as the Brazilian and Russian, so the price per carat is a little more obtainable.
When evaluating alexandrite, pay the most attention to the color change: the more dramatic and complete the shift from red to green, without the bleeding through of brown from one color to the next, the more rare and valuable the stone. The other important value factors are the attractiveness of the two colors - the more intense each color is the better - then look for the clarity, and then the cutting quality.  Because of the rarity of this gemstone, large sizes command very high premiums. There have been Synthetic Alexandrite stones produced for many decades, some of it is very close in appearance to the real thing.  We do not sell Synthetics.  To assure you that you are getting a genuine Alexandrite from us, we normally provide you with a Gem Identification Report from a reputable Independent Gem Laboratory.  The cost of this Gem Report is included in the price of the gem.  Some of the smaller Alexandrite gems may not have a Gem Report listed, in that case we will normally provide a "Statement of Sale and Evaluation for Insurance", and this report would include the specific details on that particular gem as our guarantee of authenticity.
Alexandrite is an excellent investment stone since it is a "Very Rare" gem. 
TREATMENTS - Typically Alexandrite is not treated since it would adversely affect the natural color change phenomena.
CARE - Alexandrite is also excellent in jewelry since it is quite hard, however, as with all Chrysoberyl, it should not be cleaned in an ultrasonic or steam cleaner.  We recommend Ionic Cleaners and/or warm, soapy water and a soft brush as the best way to clean Alexandrite in jewelry.
NOTE -  If you own a gem that you suspect is an Alexandrite, and you are wondering how to tell the difference between Synthetic and Genuine Alexandrite, we recommend you send the stone to a reputable Gem Laboratory and ask for a Gem Identification Report.  Prices for these reports usually start at around $100 and can be as much as $600, it depends on how much detail you want on the report.  If you don't know who to contact, here are a few links to Accredited Gem Labs:  AGA | AGL | AGS | AGTA | CCGL | EGL | GIA | GQI | GRS | GUBELIN | GUILD | IGI | LPSL | SSEF

Alexandrite is rare, a Cat's Eye Alexandrite is even more so.  This Gem is cut as a Cabochon. The stone is usually translucent with a color change of Green or greenish in sunlight or fluorescent light to Grayish/Purplish in candlelight or tungsten light.  This gemstone has a strong Grayish/Bluish White eye (chatoyancy) which reaches from girdle to girdle.
TREATMENTS - Typically Cat's Eye Alexandrite is not treated since it would adversely affect the natural color change phenomena as well as the chatoyancy.
CARE - Cat's Eye Alexandrite is also excellent in jewelry since it is quite hard, however, as with all Chrysoberyl, it should not be cleaned in an ultrasonic or steam cleaner.  Warm, soapy water and a soft brush are the best way to clean Cat's Eye Alexandrite in jewelry.
This is a Very Very Rare Gem with a great investment potential!