The most characteristic, iconic and valuable trait of the alexandrite gemstone is its color change. Alexandrite distinguishes itself from other members of its chrysoberyl family by this phenomenon: the stone is one color in daylight, and another color in incandescent or “lamplight”.
With Alexandrite, the stronger the color change, the more valuable the stone. There are two main aspects of color change:
1. How different the two colors are
The most severe color change in an alexandrite is from fire engine red to a bright green. More common are changes from purple to green, pink to grey and so forth.
2. How complete the change is inside the stone
Most Alexandrites will retain a bit of the other color in them during a color change. For example, a stone that changes from pink to green will likely still show some flashes of pink when it is green and vice versa.
The completion of color change is described as percentages from 0% to 100% – 100% being a total color change in which no trace of the other color is visible. It should be noted that this is extremely rare and most humans will go their whole lives without seeing it.