Natural alexandrite is ridiculously rare and expensive, especially if you want one that does the really dramatic color change between red and green.
I managed to get a few very tiny natural stones with limited color change, to make rings like this. I love alexandrite– besides the color change, it’s also stronger than diamond, and nearly as hard. And it’s my birthstone (well, going by one of the birthstone systems; the other one says it’s pearl, but pearls are fragile, usually cheap, and not even really stones. I like alexandrite better.)
In other news: we adopted a new pet!