Alexandrite

Alexndrites display color changes when viewed under different types of light.

This 26.75-carat cushion-cut alexandrite is bluish green in daylight and purplish red in incandescent light.

David Weinberg

Alexandrite is a variety of chrysoberyl that displays a light-dependent color change. The color change results from a displacement of some of the aluminum by chromium oxide (green to red color gradation). The stone also exhibits a strong pleochromism, in which it appears to be different colors depending on the viewing angle.