Alexandrite, a member of the chrysoberyl family of gems is one of the most expensive gem materials on the market. Due to the way the stones absorb light, the color of these stones will change from a greenish blue color to a purplish red color depending on their light source (fluorescent/incandescent). As with all gem materials there is better and worse material out there so it is possible that lower grade material will not be so expensive but nice material always carries an incredibly steep price tag.
Alexandrite was originally found in Russia (hence the name as it was believed that the first piece was found on one of the birthdays of Czar Alexander) but sources in Sri Lanka and Brazil are now producing material as well.
In gemology, stones that do things like change color or have stars in them are known as stones with phenomenon. Personally I think alexandrites can simply be phenomenal stones. It is a stone however, that requires the purchaser to have an appreciation for the unusual, and is not neccessarily the most attractive of stones. While high quality alexandrite may achieve a rich purplish red color there is always a brownish tinge to this color and while people often wistfully say that the green approaches emerald green in tone, the color is less like emerald and more like tourmaline. In reality, even fairly expensive stones will have a muddiesh color tone to them and sometimes, under some lighting situations, the two colors will sort of blend together, again leaving a somewhat blurry image. But fine material can be truly astounding (and is exceedingly rare). One of the most beautiful stone I ever saw was at the Tucson gem shows about 25 years ago where one of the dealers had a magnificent 15 or 20 carat stone that had a huge color change and was beautifully transparent. I believe that the price was somewhat over $100,000 for the stone at the time (this was 25 years ago mind you!).
It seems that the people who know about, and love, this stone always tend to be collectors. I have one customer who owns 5 alexandrites that she has purchased from me. Another customer, who is mostly a gem collector, also has one he got from me. It is, however, an expensive habit. You can generally expect to pay between $5-10,000 per carat for decent one carat size stones. Larger stones are extremely rare so as soon as you get into the 2 ct. or bigger range the price range will skyrocket.
If you are interested in owning these stones here are the things to watch out for:
1) If the stone doesn't exhibit color change it isn't an alexandrite, it's just a chrysoberyl. There are many gem "dealers" on the Internet who sell stones they claim are alexandrite but they don't have any color change so they really can't be called that (I have seen a plethora of these stones show up in the last few years).
2) There are synthetic (man made) alexandrites that are in the market that are extremely hard to detect. You need to buy from a reputable source. If it sounds too good to be true it probably is. Interestingly, synthetic alexandrite is not a cheap stone to produce so the pricing on these will be higher than many other synthetics, which often means that they won't be so much cheaper than the natural that you would immediately be aware that it is a scam.
3) For many years, synthetic color change corundum (sapphire) has been on the market and was originally marketed as alexandrite because it had a color change. The colors are usually different from an alexandrite and after you've seen a few they are easy to identify. So if someone comes to you and says they own a really big alexandrite, most likely they are talking about synthetic corundum. I don't get as many people in with these as I used to, but over the years I have had to deliver the disappointing news to many people who said their mother/grandmother/great uncle/great grandfather swore to them that this was an alexandrite, that in fact what they had was a pretty much worthless bauble.
4) As with any expensive material there are always scams waiting to happen. Lately there have been a number of incidents in which jewelers have been approached by people (I actually had an email conversation with one myself) with large (ostensibly) alexandrites (among other stones) who will claim a variety of misleading things in an attempt to sell the pieces. They will say things like: oh, this stone is so valuable that no gem laboratory will identify it. Or that it is so valuable that they can't ship it to a gem lab to be identified. This is a load of hogwash. Any reputable gemological laboratory will identify any size gem material. As a matter of fact, they love to get in large, unique gem material because it increases their knowledge of what is available. And anything of any value can be shipped through a variety of means, and if they don't want to trust a shipper, surely if you have something worth so very much money, you can afford a trip to hand deliver the stone to a gem lab.
5) While it isn't absolutely necessary, it does help to have certificates from a reputable gemological laboratory on any major alexandrite purchase.
6) Know your source. Work with someone like myself who has both a Graduate Gemologist degree and has been in business for a long time. If they are a member of the American Gem Trade Association or Jewelers of America it helps as well. There are just far too many fly by night operations who are just out to make a quick buck and the Internet has expanded their numbers exponentially.