Alexandrite is a remarkable gem. It is one of the finest color change stones in nature, resembling fine emerald or ruby, depending on the light source. It is so rare, that most people have never seen one. Yet, when the modern list of birthstones was assembled, it was listed as June’s birthstone.
... Alexandrite has a distinguished and glamorous past. It was first discovered in the Ural Mountains of Russia in 1830. The Russian imperial colors ware red and green, so it made quite a hit. It was named after Czar Alexander II’s at his coming of age ceremony.
... The original source closed after only a few decades of mining. Today they have been reopened, but only produce a few carats a year. In 1987, a new find of alexandrite was made in Brazil. Later, alexandrite discoveries were made in Sri Lanka, Madagascar, Myanmar, and Zimbabwe. However, none of these sites produces as rich and vivid a color change as the original Russian source.

Grading Alexandrite

... Alexandrite is a color change variety of chrysoberyl. The closer the colors are to pure green and red, the higher the value. The second consideration is the amount of color change. Alexandrite can exhibit everything from 100% to just 5% color change.
... Clarity is another significant grading factor. As with most gems, the majority of what nature offers us is cabbing grade, not clean facetable material. However, with alexandrite, the color change has more effect on value than clarity. For example, say you had two gems weighing a half-carat each. One gem is eye clean, with a 50% brownish/red to greenish/blue color change. The other, an opaque cab with a 100% green to red color change, would be higher in value.
... Size is always a significant factor in value. The largest alex known is a yellow/green gem weighing 74.4 carats. The largest Russian gems are about 30 carats. However, the vast majority of alexandrites are under one carat. You can see this reflected in our Price Guide. In sizes up to one carat, top quality natural gems sell for $15,000. Over one carat, the prices range from $50,000 to $1,000,000 per carat!

Distinguishing Natural Alexandrite

... We receive many emails asking what an inherited gem is worth. Most people do not realize that there are many synthetic alexandrites and look alikes on the market. Some of these have been available nearly as long as the natural gem.
... While determining the exact origin of a gem is a matter for professionals, here is a brief guideline. If the gem has good clarity, strong color change, reasonable size, and your grandmother was not exceptionally wealthy, it is most likely a synthetic.