Natural alexandrite is one of the most expensive gem materials available (at least in fine qualities). The stone is known as a "phenomenal" stone because it exhibits the phenomenon known as "color change". This means that a gemstone, when exposed to different types of light sources (usually fluorescent vs. incandescent), will change colors. Stones sold to you as alexandrite that do not display any color change are actually chyrsoberyl and not alexandrite. The color change is from a greenish tone to a very slightly purplish red tone (red is the key word here).
Alexandrite can occur in large sizes but is extremely rare in large sizes. High quality stones over 2 cts. will routinely run into the tens of thousands of dollars. They have always been expensive. There are basically only three major sources for them: Russia (which isn't a large producer anymore), Brazil (where the mine owners flooded the mine a number of years ago because of the number of deaths at the mine---due to the high value of the goods not due to the dangers of mining----this mine might have been reopened more recently but I'm not sure about that) and Sri Lanka.
So here's the deal: If you have a large stone in your possession that changes color, unless you come from considerable wealth, you most likely do not have an alexandrite.
In the 1890's synthetic corundum first came on the market. By the middle of the 20th century there was a vast amount of color change synthetic corundum coming into the marketplace that was often sold as alexandrite (both mistakenly and in an attempt to deceive). This material was routinely 1) large, 2) cut in very regular sizes and 3) exhibits a bluish green to purple color change. Let me repeat number 3: It exhibits a bluish green to purple color change. Alexandrite exhibits a greenish/red color change.
So if you have inherited a really large color change stone, and there is no red/green color change you don't have an alexandrite; you have a synthetic sapphire. It doesn't matter if it came from your parents, grandparents or great grandmother. They had these stones then too. If you bought a really large color change stone and there is no red/green color change you don't have an alexandrite.
It is an incredibly easy test to determine the difference between corundum and alexandrite. Any semi competent gemologist (and most competent jewelers) can tell you which it is in minutes, assuming they even need to test the material.
As I explained in the original article on alexandrite there is synthetic alexandrite that exhibits all of the same phenomena as natural alexandrite (as it is actually alexandrite, just made by man) on the market today. This was a much more recent development and the material is not nearly as inexpensive as the synthetic corundum. This is harder to separate from natural alexandrite because it shows the same colors as natural material. For this kind of distinction you may need a gem lab to look at the material. But again, they don't generally produce it in large sizes.
If you are interested in color change gems but don't want to pay the price for alexandrite, I routinely have natural, color change sapphires that change from a bluish tone to a purplish tone. There is also color change garnet available in the markteplace.
I do really hope that someday someone will bring in a stone for me to look at that turns out to be a large alexandrite, but it hasn't happened in the past thirty-five years so I'm not holding my breath.
I have a new pair of my jellyfish earrings out. The picture above is of the original pair but the new ones are similar.